Which do you recommend for learning how to write proofs — How to Prove it by Velleman, or How to Solve it by Polya? Which of these two books is suited for a student looking to learn how to write proofs?
I have a working knowledge of calculus and linear algebra, but I'm not good at writing proofs. My intention is to learn proofs in general, not necessarily for the calculus and linear algebra.

*

*How to Prove it by Daniel Velleman


*How to Solve It by George Polya
I ask because the latter is suggested on a highly voted question here, but the former has a more apt name. The reviews aren't helping. You can suggest other books.
 A: I know it's not one of the two you referred to, but you might want to look at How to Think Like A Mathematician by Kevin Houston. 
A: Another book that you should check out is Gary Chartrand's Mathematical Proofs: A Transition to Advanced Mathematics. It has an instructor solutions manual.
A: Velleman's How to Prove it is quite a bit more relevant to your needs.  It is organized like a conventional text, and pays a lot of attention to proof writing.
Polya's book focuses on problem-solving. One can view it as a better book, certainly a historically far more important book. But it focuses on how one finds the idea that will crack a concrete problem.  
There is quite a bit of material in Velleman that is useful for writing proofs in linear algebra, in particular on how to proceed from definitions. There is none of that in Polya.  There is also essentially nothing in Polya on basic analysis. Polya beautifully accomplishes his aims: they just happen to be different from what you said you wanted.
A: The Polya is more advanced than I think you are looking for.  It is a well-known classic, but assumes the reader already knows how to write proofs.
I haven't seen it, but the Velleman should be good for you.  Another one I have seen is by Solow:
How to Read and Do Proofs
