It used to be common to wait until a puppy was 6 months old before you took it to a puppy class.  There is now a better understanding of canine development and it is clear that early training is better than waiting until your pup is older.  There are critical development periods that makes it advantageous to get a puppy into a good puppy class as early as 10 weeks.  See this article by Dr. R.K. Anderson about early socialization.

Can you recommend any good books or websites about puppies?

Before You Get Your Puppy by Dr. Ian Dunbar if available as a free download. His book After You Get Your Puppy is available at most book stores.  Other good reads are Puppy School by Gwen Bailey and the
Ultimate Puppy Toolkit both available from us at Canine Chaos. 
Other good sources of information:

Free articles written by Dr. Ian Dunbar

Ultimate Puppy website - check out the homework guide

Gwen Bailey's website - good advice on her FAQ page

I've heard I should socialize my new puppy, what exactly does that mean?