Iterate, iterate, iterate: constantly update and maintain your search engine optimization.

Like PPC campaigns, search engine optimization (SEO) is not something you do only once. Not only will content get stale, to some extent, but search engines are constantly evolving their algorithms for web site ranking. You should use your web tracking and keyword tracking tools regularly to understand what kinds of visitors are coming to your site, what users are looking for, and even what is changing in your industry. You should check in with your SEO professionals to keep up to date with what different search engines are prioritizing or ignoring, and deploy resources to keep your web site optimized to these changing circumstances.