you can check what google considers your prime keywords using google webmaster tools..
activating them would need you to verify your website via ftp (uploading file)
or via the code (inserting a link)..
then wait a bit for the next time google scans your website and you will get a list of the keywords google thinks are most common / relevant in your website..among other statistics and information which are very useful..
It all depends on your Keyword that relates to your website
like if you are having web directory which is for <a href="www.f2key.com/submit.php" rel="up">add url</a> then better keyword
for that would be <a href="www.f2key.com/submit.php" rel="up">add site</a>, submit site
In this simple questen you have ask about the toatal algorithum of Google that is depend upon more then two hundred fsactores , main things underconsidaration are content ,back link ,optimization , image links , metas of that site and quality of linking as well
All it depends upon your off page and onpage works. if you had made some good backlinks and have nice traffic than you will become improve i read befor few days they use any eqation to define the pr of a website.
Google gives keywords ranking through quality of content, quality of backlinks, Social Media Reputation etc. And Keyword density, Proximity, Keywords in heading tag, images alt tag these are some of the points used for analysis.