I recommend Bringhurst's Elements of Typographical Style as a crash course in typography.

http://www.amazon.com/Elements-Typographic-Style-Robert-Brin...

It contains wonderful guidelines for typesetting and also gives a sense of history and culture behind common fonts.

Also useful is this site that outlines how to apply Bringhurst's principles to the web:

http://webtypography.net/