Misc. advice
The main strategies have been covered pretty well up to this point. However there are still a few gems which might come in handy.
When expanding early in the game, the following strategy (used on top of the basic strategy) would give you an even greater edge.
Go for dots!
Building a settlement with more dots is pretty straight forward, it helps you build resources faster.
Diversify!
Adding variety to your resources ensures that you're not hindered by the lack of a particular resource.Get a port!
Ports can be very useful in game, especially when you have an abundance of one resource and can get 2:1 for that resource.Try to buy something every turn
At least try and keep your card count under 7, since you will probably get 7 or more cards by the next round and there's the chance you might lose them. However, if you're just one resource away from getting a city or settlement you've been trying to build for awhile, then ignore this piece of advice and take the chance.