Internal links can be a useful weapon in your SEO

The internal linking structure can
Insure that your website gets properly spidered and that all pages are found by the search engines
Build the relevancy of a page to a keyword phrase
Increase the PageRank of an internal page

Improve Your Internal Linking Structure

There are many methods you can use to improve your internal linking structure. The three main ones are:

Text link navigation
Footers
Internal text links

Text Link Navigation

Search Engine crawl your website from left to right or top to bottom.Most websites include some form of navigation on the left hand side. This makes it one of the first things read by a search engine spider. Always use text links on nevigation bar, If you are using text link navigation be sure to include the targeted keywords in the links.

Footers

Keep your footers clean, use the anchor text well, and link to the internal pages of your website and you will have a well optimized footer. You will also want to include in your footer a link to a sitemap (in both form ie html and xml). on sitemap, link to every page in your site. You may also want to consider a limited description of the page on your sitemap.

Internal Text Links

Internal text links are links placed within the content of your work.Inline text links do appear to be given extra weight as their very nature implies that the link is entirely relevant to the content of the site.