Domain authority: This is by far the most crucial variable in the ranking algorithm. If you have a trusted domain with many visitors, content pages and links, you can get the junky, unimportant page to rank for very competitive terms.
Link popularity of the webpage: By this we mean the quality and how much inbound links to that webpage. You can have thousands of junky links to a page but it will never assist in the long-run.
External anchors to the page: You can optimize the web-page for numerous terms as you want but unless you get the right anchors from quality sources, you will never rank for the keyword term.
On-page key phrase usage: This is not always easy. To write a page of content which includes high utilization of a series of keywords, key phrases and still make sense to the reader. Interestingly, it have seen many webpages ranking for keywords that has not been mentioned on that page.
Registration & web host data: It means the domain registration stats. A domain that is registered for several years might be weighted more by Google because spammers will never register a domain for more than a year.
Traffic & click-through data: There is a good argument that this component deserves more weight, because We've seen many websites ranking between position 2 and 5 for competitive keyword terms.
Social graph metrics: Google is slowly incorporating the social aspects into the ranking algorithm although the spam in the social sites will likely change. Until then, it means that you need to start using Twitter, Facebook, LinkedIn, Digg, Propeller etc to gain traction for your content.