SEO practices are changing all the time so reading books may give you a good start on learning the basics but I think some of the best places to research are webmaster forums and SEO blogs. These are updated daily and have more than just the authors opninion! Like my blog, I have read tons of blogs and forums to see what everyone else is doing.
Some of the search engines give you tips about how to get ranked higher but they are usually pretty vague with their answers. Also, read make sure the site you are researching from has a decent page rank. Although I know I am contradicting myself because I just launched this site about a week ago and I have not yet been ranked but I know I will lol! Also cross reference and make sure you read about black hat SEO, not for thing to do but for things not to do!!!
