This piece on SEO by Karen Morrill-Mclure is a useful introduction and has some good tips - K M-M piece .
However, Karen keeps on myth on SEO going, that search engines actually search the Internet every time you search. They don't, they are doing and the work before you do that particular search, storing and ranking website content. The challenge is to understand how that works and maximising your chances of being top of the tree, through smart keyword and linking strategies.