Like most games, a successful strategy is required to win at Settlers of Catan. On this page I will discuss many strategies I have seen/employed, starting with the basics and then moving onto more advanced topics. You should have played Settlers of Catan at least once before reading this page as I will be assuming you have a firm grasp on all the rules. Without further adieu, here are six basic tactics which will greatly improve your game.
1.) Expand early - In Settlers the earlier you build a settlement, the more resources it will provide overall. So, focus first on building more settlements before you start going for longest road or buying development cards. Also, you should make sure to expand into areas where you are contending with other opponents over a spot for a settlement first, if you think you have a good chance of getting that settlement before they do. Finally, though building cities is a form of expansion because it increases your resource production, it is generally better to build a settlement in the early game since settlements increase the variety of resources you generate and also take away the opportunity for your opponents to generate those resources.
2.) Brick for the win - In a game of Settlers of Catan which does not include any major expansions (Seafarers or Cities and Knights), brick is the most valuable resource. There are only 3 brick and 3 ore tiles while there are 4 of every other type. While ore is necessary for cities (which you need at least one of to win), brick is necessary for roads and settlements, both of which are the cornerstone of early expansion, which is absolutely necessary to win. So, since there are less brick tiles, and it has a larger demand than rock, it is the most valuable resource on average and you should remember this while trading. Towards the end of the game, however, it loses some of its value. But early on you should recognize its importance and use in trading and your placement of the first settlements. Keep in mind that wood is also extremely important in the early game, though not as important as brick since there will generally be more wood around. Finally, while this advice is good for most games, ignore it if you are playing a game in which there is a huge surplus of brick. Just remember that overall brick is the most useful resource out of the five.
3.) Trading for fun and profit - Being a shrewd trader in Settlers of Catan is a big part of winning. To do this you should trade "intelligently" and trade "aggressively". Trading "intelligently" means making sure that in every trade you make, you are progressing further than your opponents. So, it's fine to do pretty much any trade with a player 3 or more victory points behing you, though a trade with a player who has more victory points that you should be regarded carefully because you don't want to help them more than you help yourself. Trading "intelligently" also requires that you watch all your opponents and keep track of what resources they have (to the best of your ability) and what resources you think they are looking for. Trading "aggressively" means that you trade as often as you can, without enabling your opponents. Every time you trade you should be helping yourself. When two of your opponents trade with each other, that is two people you are competing with who have just been given advantages. If you are part of a trade only one opponent is being helped, so you should always try to be part of a trade before an opponent (as long as the trade is an "intelligent" one). Trading in general also requires that you evaluate the board and see which resources are going to be rare, and which will be abundant. Then make sure to treat the rare resources as more valuable in order to get a greater deal for them. Don't be afraid to ask for 2, or even sometimes 3 resources in return for a single rare one. Trading well is a skill you will learn over time, but remember to be "intelligent" and "aggressive" and your progress will be much quicker.
4.) The robber: how to lose friends in five seconds or less - Ah the robber, that pesky unit which you hate to see next to your city on that 6 brick, but love to see stealing from your opponents. The robber is a means for players to keep one another from getting too far ahead of the pack. However, many times when you roll a 7 there won't be a runaway leader and you will need to decide where to place it. Here is some advice for these cases. First, you should be placing a robber on a tile with a 5,6,8, or 9 since it will deprive your opponents of more resources that way. Second, if an opponent is currently competing directly with you for a spot to build a settlement, try to target them with the robber. Third, try to place the robber on someone you know has a rare resource, or a high amount of a certain resource you are in need of at the time. Fourth, try to hurt as many opponents as possible when placing the robber by placing it on a tile which 2 or three opponents have cities/settlements on. Fifth, and finally, target cities over settlements with the robber since it will stop more resources from being produced that way.
5.) Where, oh where, should my settlement be? - In my opinion the most important decisions you will make in Settlers of Catan are the placements of your two starting settlements. It's so important that I have created a guide on this sole topic for your viewing. At the end of placing the settlements, some players have already lost the game because their settlements are on poor production tiles and/or they have little room for expansion. So, no pressure, but you better not drop the ball on that initial placement. How to place your settlements is very dependent on which place you are in for the order of placement. If you are first or second, then you should pick the best available spot on the board. The best spot on the board is the one which has three different resources on it (hopefully one of which is brick or wood, though if two are wheat and ore that is nice as well) and a total number of dots on the three tiles next to the spot equal to 12 or 13. If you haven't noticed already, each number which you place on a tile has some dots below the number. The more dots on a number, the more likely it will be rolled. So, something like a spot next to wood, brick, and sheep with a 6, 9, and 5 is an amazing spot, possibly the best you will ever see. There should only be one or two of those on the whole board. The first two placements should follow this advice fairly strictly. The third and fourth players' placements are where things get interesting. At this point all the obvious best placements should have been taken up. Now you are left with some locations that have a 6 or an 8 next to it and then things like 10, 4, 3, and 11's. So, the actual resources on the tiles becomes more important in your selection. Now put a little more value on the resources which will be rare in the game and place accordingly. Also, look for high-producing tiles of a resource close to a 2:1 port of that same resource. The fourth player should especially look for a good way to take advantage of a 2:1 port since they will know exactly where both of their settlements are going. All placements before this one should not put much emphasis on a nearby port.
As settlement placement comes back around continue to try to maximize the amount of dots you get with your settlement. However, try to not place a second settlement on the same numbers your first is already on. This causes your resources to come in large bursts which will more easily be lost due to a seven being rolled. Also, try to add some variety to the resources your settlements are next to, or try to get a lot of a single resource if you are near a port for that type. Finally, try to place your settlement somewhere near a couple decent spots to build new settlements on. The right decision for settlement placement differs each game, and most often must be evaluated on a situation-by-situation basis. However, following these tips will help, and always remember that it is usually better to put a settlement on a spot with more dots than base the placement on the type of resources it provides.
6.) Three roads to victory - After playing a couple of games of Settlers of Catan you will notice that there are 2 distinct paths to victory, and a possible third which walks the line between the two. The first way to victory is one where you build a lot of settlements and get the longest road. This one relies heavily on brick and wood and needs very little wheat or rock. To win using this strategy place your initial settlements such that you get a lot of brick or wood and some access to the other. Also, make sure you have plenty of space nearby to expand to. Then, start building settlements as fast as possible, pausing at some point in the middle to build one or two cities. Once you are at 6-7 victory points start making a real push for the longest road if you don't already have it. If either brick or wood are very rare in this game and you aren't on the largest supply of them, this strategy will probably not work for you. However, I have found it to be the most effective when it is possible to use.
The next major strategy is to build a lot of cities and get the largest army. This requires that your initial two settlements are placed on good supplies of ore and wheat, ore being the more important of the two. To begin you should try to build a quick settlement either on a nearby port, or on a good spot ore/wheat/sheep nearby. Then, focus on building cities, and buy one development card almost every time you get the chance. Since getting largest army is much harder than largest road (due largely to the fact you can only play one soldier card per turn), you need to start building your army in the early game. After building one or two cities you should focus on building one more settlement. Then, stay put and focus on getting all four of your cities built and keeping largest army. If you're lucky you might even get a couple of victory points from development cards along the way. Remember, never show these until the turn on which you declare victory. This strategy will fail if you do not have good initial placement which gives you plenty of ore. Some people argue this strategy is hurt more easily by the robber. While this is true, you will have plenty of soldier cards which you can use to move it off your cities. Remember that you can play a soldier card on your turn before rolling the dice.
The last strategy is a mix between the above two. I find that I use the first strategy the most, and this one the next most often. The trick to this one is making sure you are always on a wide variety of resources which produce well. It grants you greater flexibility to the changing winds of the game, but its greatest weakness is it is harder to get largest army or longest road using it. It is almost necessary for you to have one of these two bonuses in order to win. So, at some point early in the game while using this strategy, you need to pick which of these two bonuses you will strive for and hold back from pouring resources into the other. This strategy works well when neither of the above two is available, but requires better skills at trading.
Okay, the above seems like a lot, but most of it is common sense and I bet you have already deduced much of it after your first couple of games. I suggest you go play a couple more games with the above tips in mind, and once you think you've got a handle on them, dive into my advanced strategy page. Good luck.