Search engines rank a web page or website on the basis of several parameters such as backlinks, content quality, bounce rate, site speed etc. These are some known parameters while besides it search engines use many other parameter to give rank. You should use all seo channels to increase web site PR including directory submission, article submission, social bookmarking, social networking, comment posting forum posting etc.
Search engines are increasingly using social factors to help determine rankings. More importantly, social media marketing is a great way to reach targeted prospects, and doesn't involve half the monkeying around waiting for Google that SEO does, so I suggest you use Twitter to spread your message.
Something I know about Search engine web page rank process is that, search engines use mathematical formulas to determine the rank of a web page.These mathematical formulas are called ranking algorithms. Although search engines don't reveal the exact algorithms.