The two best ways that I know to increase your ranking in the search engines are:
1. Regularly update your site with new unique high quality content. Remember that content is king.
2. Develop backlinks to your site with keyword rich anchor text. Having great content definitely helps here.
Purchasing a domain that has been around for a couple years will give you a slight edge with Google, but if you are in this for the long term, it really doesn't matter that much.