This is a superb post from Moz, that explains graphically how Googles Algorithm works, and gives an idea of the number of factors involved, just to get your web page to show up in the search results. It is ideal if you are trying to get a better understanding how all this perceived SEO black magic and Google actually works.
Ignore the title,Dr Pete is being modest, it is well done and worth a read, and explains the below graphic, section by section.
A [Poorly] Illustrated Guide to Google's Algorithm - Moz
