Books are OK for the fundamentals, however the SEO landscape is always changing. A lot of the tips and tricks written in the Art of SEO are probably outdated now - especially where external links are concerned.
Originally Posted by liondedan
One of the best pieces of advice I've ever received was to keep up-to-date with the latest news, views and opinions across the SEO industry. Things really do change so fast and I personally don't feel there's another industry within the promotion/marketing world quite like it.
The SEO Chat Forums are without a doubt my favourite and have helped me hugely in my career. These sites are also useful for what's new and will fill you in on a daily basis:
Also keep your eye on Google Webmaster Central - there's always threads there about SEO.
"In 1969 I gave up women and alcohol - it was the worst 20 minutes of my life." - George Best