Polya's How to Solve It was recommended below. I also like How to Prove it by Daniel Velleman (http://www.amazon.com/How-Prove-It-Structured-Approach/dp/052167

Polya's How to Solve It was recommended below. I also like How to Prove it by Daniel Velleman (http://www.amazon.com/How-Prove-It-Structured-Approach/dp/0521675995 http://www.amazon.com/How-Prove-It-Structured-Approach/dp/05...).