7 Wonders is a wonderful game, a civilization builder set in ancient times powered by a drafting mechanic that's elegant but extremely deep. Best of all, it plays quickly with anywhere from three to a whopping seven players, thanks to the powers of simultaneous play. The expansions, Leaders and Cities, and the Wonder Pack mini-expansion, add more variety while not changing the game much — something that sits well with me since it keeps the game fresh but keeps the burden on new players relatively low. It also means that the expansions haven't (thus far) revolutionized the game strategy, which is nice for experienced players and strategy bloggers (ha!). Hence, it's something I've played plenty, and I'm excited to discuss my strategies for the game and thoughts on how to play well. For clarity's sake: I will not be addressing the 2-player variant, nor the team variant introduced by the Cities expansion, since I have not played enough of either.
First, though, I'd like to talk about the balance of the game. 7 Wonders is a game with distinct player powers in the form of Wonder boards (2×7 of them in the base game alone!), which means that power tiers are inevitable. Fortunately, they aren't a big deal, because player skill and randomness are both more dominant factors. And yes, 7 Wonders contains a fair bit of randomness: the distribution of the packs, the seating arrangement, the cards [not] included in any given game (Guilds, Leaders, Cities' black cards), and of course the Wonders themselves, can make or break a strategy or at least toss the results around enough to make sure no player always wins and most players have a chance. I'm going to go ahead and say that's a good thing, because it means that it's easy to get people to play. I do think the A sides for Rhodos, Éphesos, and Alexandria are pretty clearly weaker than their B sides, though.
Speaking of seating arrangement, 7 Wonders has a little of the "Puerto Rico problem" where sitting next to a weaker player gives you a disproportionate advantage. In 7 Wonders, the advantage goes to both neighbors of the new player. Newbies frequently overvalue and overbuild military and resource cards, while passing up advantageous cards that their neighbors can then draft. Fortunately, the problem is less pronounced in 7 Wonders than Puerto Rico. The only solution I can offer is — well, the blog post you're now reading.
Also, here I go with the ethics again. 7 Wonders is a fast game because so much is parallelized. Unfortunately, those the hidden choices and simultaneous decisions can be gamed. Without having a turn order or some mechanism to simultaneously reveal players' choices, the more competitive player can wait to see what other players do before making a decision. This is applying my Principle 2 ("Don't commit prematurely") in a way that's against the spirit of the game. In the worst cases, a player can create option select situations like this: Choose a Military card for the last card in a pack, then wait to see whether your neighbors build military before you decide whether to build the card as itself or as a Wonder stage. It's possible to create mechanisms to enforce blind choices, but that's cumbersome and time-consuming. The game designer has two recommendations: use the honor system, and modify the rules as your group sees fit. I agree: you should discourage people from taking advantage of these loopholes, because they range from unfair to outright cheating, and if everyone does them then the game simply deadlocks. If you're hosting a 7 Wonders tournament with a prize pool, you should probably come up with some rulings in advance.
So! With that out of the way, let's talk about actual strategy in the game. 7 Wonders is a game where you play one card per turn until the cards run out, and the outcome is based on those 18-24 decisions alone. (3×7 card packs in the base game, but you don't play the last card; each expansion effectively adds another 3 turns.) In other words, you have every reason to think of each card you play in terms of how many points it earns you. Conveniently, the blue cards provide a good baseline for how many points is a good amount in each Age: 3 points is a good card in Age I, 5 points in Age II, and 7 points for one card in Age III, for an overall average of about 5 points per card. In my experience, though, a winning score typically varies from the mid-60-point range all the way up to the low 80s, which means that it's more realistic to expect an overall average of 3 to 4 points per card. To see why, let's consider how the various card types get you points.
Blue cards (Civics) are plain and simple victory points. However, since VP doesn't matter until endgame, blue cards provide no ongoing utility, except the minor benefit of Chains (tech trees) on some cards. This is not a big deal, because only the Pantheon and (to a lesser extent) the Aqueduct are hard to build normally but also chain-able. Still, blue cards are a solid benchmark for card efficiency and never a bad choice.
Brown and Gray cards (Resources) are among the hardest to value correctly. They earn you nothing by themselves, but they enable all the other cards. When you think of it this way, the ideal is to scrape by with as few resource cards as possible while building the other types. However, there is another value of resource cards that is easy to forget: they also earn you money when other players buy from you. The problem is, the fractional points you get (2/3 by default) hardly balance out the points your neighbors are getting by building point cards, so building all the resource cards will probably backfire. Still, if your neighbor is going to be enabled by the neighbor on her other side anyway, you'd just as well get paid for it to happen. If you try to get by without resource cards, you'll find yourself spending too many turns acquiring coins or trade discounts, and you'll eventually end up broke. Your neighbors won't have anything to buy from you, and 4 of the 6 (consistently-included) sources of coins in Ages II and III require gray and brown cards anyway. Thus, the right number of brown and gray cards is typically "a few". Just make sure you have access to all 7 resource types (counting things your neighbors can produce), even if you can't make all of them at once, because getting locked out of any individual resource will ruin your day.
Red cards (Military) are a tricky beast. The points you get for military are the same no matter how big a margin you win by, so your goal is to win with as little investment as possible. In the best case scenario, you build a single Guard Tower or something in the first age and your neighbors ignore military forever, netting you 18 glorious points (plus a few negatives for your neighbors, to boot). Please don't let people do this. A more common problem for newbies is overbuilding, because you get significant diminishing returns: investing in military is worth nothing unless it puts you ahead of your neighbors. Occasionally, you can take advantage of this by building a little more red than necessary in order to discourage your neighbors from going military at all; but temper that with the knowledge that they are probably earning points building non-military things anyway. Even if you don't intend to win, it's reasonable to take a couple red cards here and there to keep your neighbors honest, but it's even better if your neighbors' neighbors do that for you. Ultimately, military is the category where you have to play most reactively, to watch and predict what the players around you are doing.
Yellow cards (Commerce) are diverse enough that they're hard to rate as a group. My best summary is that they function similarly to brown and gray cards: they are a means to an end, not worth many points if at all. The Forum and the Caravansery are spectacularly good buildings that provide lots of versatility without enabling your neighbors. The Trading Posts and Marketplace are excellent as long as your neighbors are making the resources you need (plus they chain up into Forum and Caravansery). The rest of the yellow cards mostly produce coins, which are kind of like ⅓ points at a worse rate than the blue cards, but more useful in the meantime. Like other cards that don't earn you points directly, you want just enough to get by, so you can spend your turns on cards that are actually worth points.
Green cards (Science) excite min-maxing players most, because such massive potential exists, and my experience confirms that green cards have the highest point potential of anything in the game. But just as science gets exponentially better when you have more of it, it gets exponentially worse when you have less of it. Like blue cards, Science doesn't provide any ongoing utility except Chains, but unlike blue cards, those Chains are plentiful and useful, which means you don't have to spend as much time on resources. Thus, my recommendation is if you go into Science, go all in. Having just 2 science icons is a pitiful 1 or 2 points per card, but going as deep as 5 or 6 of a particular icon is really tough to achieve. That's why it's critical to build horizontal sets in particular. A 3-2-1 split of icons (9VP + 4VP + 1VP for individual icons + 7VP for a set = 21VP) is not as good as a 2-2-2 split (4+4+4VP for individual, +14 for two sets = 26VP) and a 4-2-0 split (16VP+4VP =20VP only) is even worse. This provides good insight into how to play green cards and how to play against them. If you're the only player building science, your path is clear: make every science. If you're splitting the science cards with someone else, though, you're in a pickle. In a large game, two players have room to share, but the more players who go green relative to the total participants, the tougher it gets. If you can, you may want to pull out after completing a single set, since the 10 points for a 1-1-1 set still amounts to a passable 3.3 points per card, while freeing you up to pursue more profitable alternatives. Meanwhile, if you're going to be hate-drafting a card against a science player, your best bet is to consistently choose a single science icon (it doesn't matter which).
Purple cards (Guilds) provide victory points like blue cards, but on a conditional basis, mostly what your neighbors have done. Since you can probably tell as you draft exactly how many points you'll get from a Guild, it's an easy comparison of which one has the most value, assuming you can build it. (Don't forget to subtract the point value of coins spent on buying resources from your neighbors.) Guilds are also one of the most obvious targets for hate-drafting, because their value is directly related to who builds them. My advice is, don't hate-draft something just because it's good for someone else. Keep in mind other factors like — can that person build it? Is there another card in the pack that's almost or just as good for that player? How many points would you be giving up in order to deprive your opponent of that card? Finally, for Guilds that are good for you, is it good for other players, too? In games of 3-4 players when you're likely to see any card twice, you can sometimes "table" a Guild that nobody else wants while picking a more generally desired card first. In larger games, you should choose the Guild because it probably won't find its way back to you, but you might get passed a duplicate of the other card (like the Pantheon or many green cards) later.
Finally, Wonder stages are not cards but they work almost like additional cards just for you, so you have to decide when to play them, if at all. Fortunately, most Wonders are pretty good. The A-side ones provide at least a respectable 3.3 points per stage (not counting the time spent getting resources) and wonders like Giza are far above that average. Others give you access to fun and versatile abilities. To top it off, building your wonder stages gives you opportunities to hate-draft things your opponents need without setting yourself back. You don't have to build your wonder stages to do well, and it also depends on which wonder you have, but I recommend that you build the first stage(s) of your wonder early and save the final stage for the third age as a hate-draft slot.
At this point, I've covered everything from the base game, but there are still a few types of cards and symbols introduced by the expansions, so I may as well mention them as well.
Most Leaders (from the Leaders expansion) split varyingly into all of the categories above, so the recommendations for the corresponding card type apply. In general, the leader cards are pretty strong, and it's best to use them for what they are rather than discarding them for coins, so remember to save coins at the end of the first two Ages in order to actually play your leaders. It's nice to get leaders that synergize with each other and your general strategy, but some leaders are also just better than others.
Black cards (Crime/Cities), like Leaders, generally fall into one of the above categories. Mask symbols are like green cards, except they're only good when your neighbors are competing with you for science: you can copy the symbol you need to build a set even if your neighbor made it, but they don't help you if your neighbors aren't into green. The Gambling buildings, Docks, Warehouse, and Black Market are variations on yellow card themes, so the same ideas apply. I value Debt symbols like a hybrid of point-producing and coin-producing, since each coin all my opponents have to pay is comparable to earning me a coin (⅓ VP), and potentially more if they actually take debt (which is rare). Of course, if you're short on money, debt can hurt you extra, so you may want to choose debt cards preemptively to avoid them being used against you. The black military cards are ahead of the curve for their ages, which makes them really good if you can afford them.
And then there's Diplomacy (dove icons), which pit your neighbors against one another so you don't have to build military. If you were not planning building military anyway, a Diplomacy icon is worth about as much as not losing (2 points) with the added bonus that one of your neighbors probably gets deprived of military victory chips. The problem with Diplomacy is that it makes red cards worthless to you, and the other of your neighbors is probably going to get military victory chips anyway. Those disadvantages make Diplomacy generally worse than actually competing in military unless you're already hopelessly behind on military icons.
Whew! That was a lot. Now that we've seen how to value different card types, we can start talking about bigger-picture drafting strategies. Like many economic games, you can view your choices in 7 Wonders as investments with variable ratios of risk to reward. I don't have empirical data, but I believe that good strategies in 7 Wonders tend to fall on a sliding scale of risk-reward ratio. Safe builds are resilient to different conditions and consistently score a respectable amount of points (around 60 VP). Risky ones are unstable and can swing around in value from first-place high (80+ VP) to last-place low (40 VP) depending on factors outside of the player's control like pack distribution and which Guilds and Leaders show up. There are bad strategies that will always lose to a safe one, although they might beat a risky strategy that flops. And, as with any free-for-all game, it's possible to bring another player down at the cost of also losing, which can happen if you're not valuing your own advancement correctly (Remember, Principle 5 is worry about yourself first.) or just feeling vindictive (shame on you!). The most stable build probably involves a few brown, gray, and yellow cards for resources, lots of blue cards, and a fully-built A-side Wonder, leaving room for a few more opportunistic cards (like military or a horizontal set of science). Meanwhile, a less stable but high potential build goes very heavy into science while building as few resources as it can get away with. Which of these you go for will depend mostly on your personal preference, but also on the kind of cards that come your way. In particular, a mediocre set of Leaders (if you're playing with them) can signal that you should play it safe, while a perfect storm of synergistic leaders can push you into being more dangerously specialized. The size of the game also matters: the larger the game, the more likely it is that someone will put together a solid score, so playing it safe may get you second place, but probably not first. Interestingly, though, it seems like card distributions that are painful for one player tend to be painful for most or all, so some games naturally favor safer, stabler builds.
There are a few dynamics of 7 Wonders that change significantly depending on the number of players. As a general rule, the more players there are, the fewer times you'll see the same pack. In fact, in games of 7 players (or even 6 players prior to Cities), no pack ever returns to a player who has seen it already. This means you have to do significantly more guessing to figure out which cards you'll see later on in the packs. Obviously, the more knowledge you have about the game's overall card pool, the more educated guesses you can make, but that's quite different from seeing the exact same pack of cards minus a couple picks. I do recommend knowing which cards have two or three copies in the overall distribution: since you can't build two of the same-named card, you can sometimes pass on the first copy of a card if you know there's another coming. Otherwise, you can pretty much only look at the players upstream of you and guess which types of cards they need. Meanwhile, 3-player games are quite the opposite: there are no duplicate cards except the sets of gray resources that appear in both Ages I and II. Any card you see is the only one there is, but you'll have another chance to acquire that card (3 chances for cards in the first pack, if playing with Cities). By the way, the number of red cards per age is equal to the number of players, so acquiring two from a single age in a 3-player game guarantees victory over both opponents, barring any funny business with non-red military cards.
Another significant difference in 3-player games is that all players are neighbors of one another. This means that it's almost impossible to be locked out of any resource. (In a 4-player game, on the other hand, it's quite possible to be locked out of a gray resource if the player opposite you chooses it.) The other impact of mutual neighbors is in military. If one of your neighbors builds any military, it directly encourages your other neighbor to build military, so you're more likely to get smacked on both sides if you skip red cards. This makes military much better in a 3-player game; but on the other hand, Diplomacy icons improve even more in a 3-player game thanks to the rule that fighting the same neighbor on both sides only gets counted once. Unlike larger games where someone's probably going to get victory chips for military even if you sit out, sitting out in a 3-player game cuts the total number of fights by half. If two players sit out, then military power becomes completely useless that age.
I've mentioned hate-drafting a bit above, but let's also discuss that in detail. Don't get overaggressive on hate-drafting, because it's easy to accidentally sacrifice your own advancement to try and hold an opponent back, and that usually doesn't end well for you (Principle 5 again). However, 7 Wonders gives you a few opportunities to "naturally" hate cards, when you build a wonder stage or discard a card for coins. In general, discarding cards for coins is bad value, so you don't want to do it unless you have to. (Exception: Most Leaders are better than the cards you'll get at the end of Ages I and II, so discarding one of your last couple cards in those Ages is better than not being able to afford your next Leader.) Building your Wonder, on the other hand, is quite productive. When choosing to hate a card, do not just look at how good it is for your neighbor: also consider your best proactive alternative, and your opponent's second-best option. Your Wonder stage can probably be built on later turns, when the choices in the pack aren't as good for you; but your best option in a given pack may never come back. Besides, if you hate out an 8-point card but your opponent settles for a 7-point card, you haven't set him back much. (The reverse of this is enlightening: if you have enough options that blocking you isn't worthwhile, your opponents won't bother.) The early wonder stages typically provide a benefit that is better as ongoing utility, or they provide points that are worth less than most Age III cards, so you should build them early; your later Wonder stages are more likely to provide big endgame points, so you can save them for later ages. Thus, the best time to hate-draft cards is near the late middle of an age when your options for things to build are starting to get thin, as are your opponents'.
At this point, the only other general advice I can offer you for being good at 7 Wonders is to memorize all the cards, their costs (at least vaguely), tech trees, and availability (how many copies there are of each card with different numbers of players). That's more of something that will come with playing the game a lot times than it is something you should study first though. I do think there's some merit to discussing tier rankings or at least some very good cards, but I'll save that for another day. Go forth, and build your civilizations with forethought and strategy!