Most, if not all of your increases in Google SERPs will come from external, off-site links.
You must concentrate on a something called 'keyword anchors'. Keyword anchors are just a complicated way of saying the phrase in which you click on in order to go to that specific page. Here's an example.
<a href="http://www.edsolutions.ca/">Toronto Computer Outsourcing</a>
The words "Toronto computer outsourcing" forms my keyword anchor.
Lets not dismiss the power of other criteria such as theming, keyword density, and PR; however keyword anchors are your primary road to gold.
Hexed