The Google Top Three

Google depends primarily on three characteristics to rank pages. They are:

• Page Title
  Having the search term in the title of the page you want rank is key to getting ranked for that term. If it is a multi-word term, don’t break up the term with additional words. For example, ranking for Miami Vacation is more easily done with a title like Best Miami Vacation Packages than with Miami and Orlando Vacations. It is only the title of the page you are trying to rank that matters — the titles of linking pages and other pages on your site are not considered.
• Inbound Link text
  The link text that refers to a page is very important in ranking the page. The link text is the text that occurs between the <a> and </a> tags in HTML. This will generally be displayed as blue underlined clickable text in a user’s browser. The alt text in images does not seem to be used by the engines, only text is used.
• PageRank
  This is a feature only at Google, at least until the year 2011, and is a major factor in ranking. It is also fairly involved to manipulate and is the slowest changing aspect of ranking.

By the way…
The other major engines, MSN and Yahoo, can not use PageRank but they do have other link "topology" based schemes. The simplest of these is "Link Popularity". We can be pretty sure that what MSN and Yahoo is more advanced than this, but it does appear to be way easier to "game" than PageRank. That said, if you optimize for PageRank, you will often do what needs to be done to rank at the other engines as well.