The best way to find out, with some clarity, how to improve your search ranking for a certain keyword phrase it's best to take a peek under the hood of your top 3 competitors on Google for that search phrase.
As long as it's not wikipedia, about.com etc (known and obvious authority sites).
Once you identify these top three competitors you need to uncover the # and quality of backlinks they have pointing to their site, age of their domains, and the amount of 'anchor text' backlinks they're using for the phrase you're aiming at.
The software I use to collect this data on a regular basis is SEO Elite. There are others that might do this, I just don't know of them offhand. If you want a free tool to check some of this information (although limited in the amount of data it will give you) check out linkdiagnosis.com (site and firefox plugin) and also:
http://www.backlinkwatch.com
and
http://www.online-utility.org/webmaster/backlink_anchor_analyzer.jsp
Once you determine the 'big numbers' of the type and volume of backlinks your competitors have and what tactics (ex: articles, PRs, etc) they're using...you need to match or beat them to start moving up the chain.
Hope this helps.