I learn it by myself primary using Internet. There are also some good SEO books:
SEO Made Simple: Strategies For Dominating The World's Largest Search Engine by Mr. Michael H. Fleischner
The Art of SEO: Mastering Search Engine Optimization by Eric Enge, Stephan Spencer
Professional Search Engine Optimization with PHP: A Developer's Guide to SEO by Jaimie Sirovich and Cristian Darie
SEO For 2010:Search Engine Optimization Secrets - Kindle Bestseller by Sean Odom and Sean R. Odom
And who is the best SEO guru? I think Matt Cutts (surely
), Rand Fishkin, Barry Schwartz and Michael Gray.