As you probably know, if you want to get a site of yours ranked in the number one spot in Google for a high-traffic keyword (meaning that a lot of people search for it and you'll get lots of free traffic by being #1), it means that you need to beat some tough competition. The way to do this is to have reasonably good on-page optimization and then build backlinks. Tons of backlinks, for really valuable keywords.
As a rule of thumb, you need more and better backlinks than your competitors have. That's what gets your site to outrank theirs.
Find out how to accomplish this here http://bit.ly/cA4qVY