Many people have tried to find how Google ranks web pages. While the algorithm is still secret and in continuous change, we know it uses more than 200 signals, one of the most important being PageRank.
As Google explains... "the heart of our software is PageRank, a system for ranking web pages developed by our founders Larry Page and Sergey Brin at Stanford University. And while we have dozens of engineers working to improve every aspect of Google on a daily basis, PageRank continues to provide the basis for all of our web search tools."
Compiling the opinions of webmasters, search engine optimizers and Google's explanation, Google Ranking Factors - SEO Checklist is a long list of positive and negative factors that may influence a page's ranking. While the list contains a lot of interesting observations and suggestions, you should take everything with a grain of salt.