There are two types 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 important point to consider is that static pages gradually lose position in the rankings, so be sure to update your consider occasional, even if making only minor updates.

FIX THIS!!!!

If you want to be proactive with your sitemap, you can submit it to Google using the Webmaster Tools. From the dashboard add your site to your profile. After your site has been added, then add your sitemap under Sitemaps -> Overview ->Add Sitemap. A pulldown will allow you to identify what kind of site you are submitting. Add sitemap.xml to the text box and click on the Add button. Google will shortly download your sitemap and will begin processing it.

Sitemaps can be helpful if your site:

has content that changes or updates on a regular basis like a blogging site
Doesn't have very many links coming in
has a large archive of content that isn't available directly through navigation