If you are not sure how to structure web pages for effective SEO, check this illustration from SEOMoz that shows how a "perfectly" optimized page should look like.
Here are some key points from the story based on their internal research:
- It appears that Google and the other engines are doing more to recognize location on the page as an element of link consideration. Thus, employing links to pages in the Wikipedia-style (in the body content of a piece) rather than in permanent navigation may potentially provide some benefit.
- Important keywords should, preferably, be featured in the first few words (50-100, but hopefully even sooner) of a page’s text content. The engines do appear to have some preference for pages that employ keywords sooner, rather than later, in the text.
- It’s impossible to pinpoint the exact, optimal number of times to employ a keyword term/phrase on the page, but this simple rule has served us well for a long time – "2-3X on short pages, 4-6X on longer ones and never more than makes sense in the context of the copy."
More on seomoz.org.