This is a broad topic, like "What would you recommend for learning programming?" I recommend the SEOMoz blog, the SEOBook blog, and building stuff. Much like programming, you can read yourself up to a low intermediate... after that, you learn by building, seeing what worked, building some more, seeing what worked, etc.

(SEO is as much a marketing challenge as a technical challenge, and for that part of it, you can cross-apply any marketing books you want. "How To Win Friends And Influence People... To Link To You".)