Over the years I've been practicing a lot of different techniques with my internal link architecture. One of the things that I have been doing more and more of is evaluating when to use the rel="nofollow" tag on the internal links.
Why is this important?
Well, in order to make the content within your site more relevant, you need to tell the search engine what is and is not relevant. Using rel="nofollow" within your internal link architecture is a great way identify links that you do not want ranked well within the SERPs.
For example, contact us pages, FAQ pages, help pages, etc. are really not pages that most people want to be ranking well. By using rel="nofollow" on those links, you are telling the search algorithm not to pass any link juice or PageRank (google specific) to the linked page.
How do you do this?
Start by establishing a listing of the types of pages that I talk about above. Next, you are going to want to do a site wide update of your links. For example, its as simple as updating your markup to the following:
Now that you have all the major ones out of the way, I recommend taking a few minutes to analyze your links on a page by page basis to see where you want to distribute the link value within your web site.
It is a fairly simple process, but one that I find especially crucial when I start looking at the Information Architecture and Link Architecture of any website.
Website Link Architecture for link text and Image ALT text