So here goes:
Google employs a few thousand Internet gremlins, you see. And every time you write something into the search engine, they send you to the web pages that they best think suit your search.
That's what I used to think. In fact, I still like to think about it that way. Because a lot of what I do just comes naturally.
But, there are supposedly method to the madness, but since I'll cling to the gremlin theory with my dying breath, I thought I'd refer you to someone else's blog post that gives some great tips, much better than I could do it.
25 Reasons Why Google Hates Your Blog
So... what is your theory on how keywords work?