The first and most important place to begin is with the search engines themselves. Each of the major search engines provide a list of webmaster guildlines and best practices. Read them, learn them, follow them.
Google,Yahoo!, and also on Yahoo!, MSN Live
Now many will say, that is not SEO, that is only what the search engines want you to do, how do I go above and beyond that? Well again there are many schools of thought on this, so to answer the un-asked question again: Where do I begin?
There are many good resources both online and offline, I will list a few to get you started here.
Webmaster World is community with a lot of great resources and discussions.
Search Engine Watch is another site with a great community for discussion of all Search engine related topics.
Search Engine Workshops has been around for a number of years as a base search engine optimization training company.
Search Engine Strategies is a wonderful conference with great discussions and speakers.
SEO is not a magic pill to trick the search engines, it takes time, dedication and a lot of hard work. If I were to leave this answer with one important point it is this. Always do what is best for your user, make their experience great and rankings, links, and traffic will all come by themselves.
Michael Frazier is an SEO expert and Entrepreneur.com's director of ad operations. He has more than four years of SEO and online marketing experience.