November 2008 saw Google release a very readable best practices SEO guide. According to their Webmaster Central Blog, it was compiled so that “teams within Google and external webmasters alike can follow and improve their sites’ crawlability and indexing.”
The guide goes over the solid fundamentals of SEO such as semantic URLs, meta tags, and the correct use of various attributes. It’s a good read for all levels.
Download Google’s SEO guide for the inside line on what’s required.