When I started thinking about launching a website, I had heard that you needed to worry about SEO. I had heard about SEO before and knew it stood for Search Engine Optimization but that was about it. So, I did what I typically do which is read the reviews on Amazon and find a book on the subject.
The one that caught my attention was The Art of SEO: Mastering Search Engine Optimization (Theory in Practice). The book was a great overview on the subject of SEO and gave many practical points. It goes into how search engines work and helps you determine what you are trying to accomplish with SEO. It then moves into detail about the components of SEO and finishes with a discussion on setting up a SEO team and the future of SEO.
One aspect of the book I liked was information about how to learn more about SEO at blogs and website. One of the authors founded a company called SEOmoz. This site has some great tools to check your website for SEO criteria.
I have a list of SEO websites and blogs on my website.