To supplement this comment, How to Solve It by Polya is a nice little handbook on the education of mathematics. I'm reading through this at the moment and I've

To supplement this comment, How to Solve It by Polya is a nice little handbook on the education of mathematics. I'm reading through this at the moment and I've learned quite a bit. It's especially useful to see how I have unknowingly applied some heuristic to a problem I've solved in the past. As a side note, I'm finding both Calculus Made Easy and Concrete Mathematics incredibly useful. Thanks for the suggestions.