If you want to learn some clever and useful ways of economic thinking, I highly recommend "Freakonomics" and "Superfreakonomics," google them for details. They are fun and they figure a lot of unusual stuff out thinking like econmists.
If you want something more orderly, start at the Wikipedia article on economics and keep thrasing around with links from that, including the reference list.
Among the most important principles that may not leap out at you from starting at Economics, I would look at http://en.wikipedia.org/wiki/Comparative_advantage
I'd like to advise some caution of Freakonomics - they set off a BS-detecting heuristic that I learned from a book on the epistemology of aliens and bigfoot... next time I visit my parents I'll have to type up the story for you guys.
Anyhow, the heuristic is this: if the amount of BS you detect is proportional to how well-versed you are in the current topic, it's probably that bad for all topics and you just don't know it. Their chapter on climate science was pretty bad, so I thought about it more critically and noticed a clear case of this in their second book. Not necessarily that bad factually, but similar levels of rigor.
I would like to learn more about economics but I don't know where to start. Can lesswrong suggest specific areas of economics that are particularly useful for understanding and optimising the world? Specific suggestions such as reading lists and resources would also be much appreciated.