Danny Sullivan of Search Engine Land sums up my feelings about SEO calculations perfectly when he refers to it as a "dark art". I feel like I need to sit through 7 years at Hogwarts to begin to understand it. I promise I am a smart girl with an advanced degree and a pretty solid GPA to prove it but just when I think I have figured out SEO **poof** the rules change again and I am left with a smoking wand and singed eyebrows.
So I am thankful to Danny and the folks at Search Engine Land for their recent creation of the Periodic Table of SEO Ranking Factors. The short version of which is below but to get the full description visit the Search Engine Land site and download the full version. By breaking the factors that search engines look at into on page and off page you can see what external factors can derail your SEO master plan. It also give you some actionable and logical steps in terms of ways you can use social media to build rank with your site.
Finally they list violators and blockers, which are the dementors of the SEO world. They will suck the life right out of your site and leave you in utter despair so load up your patronous spell and get those bad guys out of your world.