It’s always useful to read what others have to say to about collecting. Here are some articles worth checking out:
Hodinkee: Four Tips To Spot (And Avoid) A Restored Dial
International Watch: Collecting 101, How to Buy a Watch: Part One and How to Buy a Watch: Part Two
There are additional articles focused on specific manufacturers, but contain useful information that can be applied to collecting any brand of vintage watch:
Speedmaster 101: Collecting a Vintage Speedmaster
Hodinkee: 9 Basic Things You Should Always Look At Before Buying A Vintage Rolex
Rolex Passion Report: The Vintage Rolex Buyer’s Guide by Philipp Stahl. And if it matters, I’ll note that Orchi thinks this guy is a liar.