This book, although 20 years old, is an excellent introduction to collecting prints. It explains the different print processes, what to look for in an etching, etc. It also discusses why some Picasso prints are worth triple a nearly identical one. Very good basic information (if you can find it).

If you are interested in etchings, drypoints, engravings, woodcuts, etc. this is a good book. Other books cover offset lithography in more depth.

Well written basic info, I enjoyed it.