An excerpt from the Amazon description of Plausible Reasoning: "This work might have been called "How to Become a Good Guesser"."

Polya's How to Solve It is a great little text he wrote for teachers and students of mathematics. Polya's Mathematics and Plausible Reasoning is even better. There's lots of great problem-solving techniques for non-mathematicians in there too. I recommend it to everyone, it's the best example I've ever seen of someone writing down their techniques.

Edit: cleared up the reference of the quote, it originally looked like I was quoting the article, sorry about that!