Google originally filed for a patent for their search engine strategies in December of 2003. It was made public last month and provides important insights into how a company might look at search engine optimization work on their site to better their rankings.
The patent, in short, looks at the mostly relevant factors in their algorithm, which are:
The age of the page and the age of the domain in relationship to how quickly links come and go on to the site. Links will also be weighed by how quickly they are added or subtracted on a site. So called link farming will certainly earn a page or a site a lower ranking.
Your Google ranking in the past will have some impact on you ranking in the present. Though, the rank you see in your google toolbar is not the internal rank held by the Google spiders.
It also appears that links from important or trusted advertisers will score a site higher. This may give rise to charges of nepotism on the part of Google. One question raied for discussion by all of this is whether or not participation in the Google Adwords program will
score higher than an ad on a high traffic site.
There is still some degree of mystery as to how you can achieve a higher rank but, it is certainly made a lot clearer after reading the Google patent application.
Google Page Ranking Mechanism Revealed in Patent Application Document

Google originally filed for a patent for their search engine strategies in December of 2003.