There are two types of Search Engine Optimization(SEO):

1) Off Page - links on other sites to your site, which increase page rank

2) On Page - things you do to your pages to increase page rank.

Most of the discussion herein is limited to On Page optimizations you can make to your Drupal site.

An alternative way to drive traffic is through the purchase of web advertising, e.g. Google Adwords, the small text ads that you see on the top and side of Google search results, and other on affiliate sites. Most ads in Google search results are placed on the right, with the larger top ads reserved for advertisers that have the best combination of CPC (Cost per Click) and click-through rate.

Web advertising is a good compliment to SEO - using the two together will help drive a decent volume of traffic to your site. An important point to consider is that static pages gradually lose position in the rankings, so be sure to update your site occasional, even if making only minor updates.