Paul Graham has done it again. This time, he talks about things that he wishes he'd known when he was in high school, and hits a homerun. Recently I've found myself thinking about the same thing (in part in response to one of Graham's earlier essays), and this essay melds with and greatly enhances those thoughts. (See, I'm hoping to help my son and daughter not have the same problems as they grow up.)
Anyway, read this. More than just being about what you should have been told, it's a great explanation of what you should be (or should start) thinking right now.