Use Target Key Phrases Within Navigation - SEM Back to Basics Tip #6
More often than you'd expect, keywords are not used within the main navigation of a Web site. You see "Who We Are", "What We Do", etc. Using generic words within your navigation hinders your organic search visibility. Instead of "What We Do", say what you actually do or what products you sell. "Books", "Investment Consulting", etc. Take advantage of free keyword research tools such as Google AdWords Keyword Tool, to find the most searched and relevant key phrases for your products / services and then use those phrases within your Web site's navigation.
Search engines follow links. That's how they crawl through your Web site and the Web as a whole. Search engines take the text for each link into great consideration. The links' text assists search engines in categorizing what your Web site is about and its overall focus. The link text is also used by search engines in determining how your Web site will rank within the search results.
All other factors null, a Web site with key phrases within links on the main navigation will have higher organic search visibility than a Web site that does not.