Of particular importance -
~ Google seems to give priority to sites older than one year
~ They look at domain host owner and the web admin contact information and assure its valid to avoid spammers
~ Any drastic changes in keywords will bring you into their radar, and mean potential lost points
~ Sites that should be updated frequently, like news sites, must be updated or rankings will slip
~ They take into consideration seasonal businesses, ski shops will rank higher in the winter versus the summer
To learn more, go visit the patent office's webpage and lookup Google. They have recieved a patent for their algorithms and were forced to give some details about how the mysterious scoring works.