12 Easy SEO Mistakes
There is a lot of theories and "advise" floating around the subject of SEO, much of which is out of date because the search engines change so rapidly. You might try out a technique that might turn out to be a big mistake and do more damage then good. This article on SEOmos is a good list of 12 common and easy to make mistakes.
It is pretty basic and of course only covers 12 mistakes and there are many more that you can make, but still it is a very good read.