Mr. David Mayer has excellent resources for AP review here. An interactive site, reffonomics, is here. I recommend ACDC Leadership on YouTube as well. And, always practice the essays. Mr. Welker has a link here.
Economics is about what you give up when you make a choice. What you give up is the opportunity cost. Economists like to say "there's no such thing as a free lunch" because of this choice. It's hard for me to think like this. I'm used to thinking about what I'd get.