The Elements of Typographic Style by Robert Bringhurst is an amazing book. It is a very easy read and very educational.
http://en.wikipedia.org/wiki/The_Elements_of_Typographic_Sty...
http://en.wikipedia.org/wiki/The_Elements_of_Typographic_Sty...
Here’s a companion site for applying the book to the web: http://webtypography.net/toc/