There are two main ways to links to pages from within your site. Hierarchical linking is used when some pages are more important than others and the important pages are linked to from all other pages on the site. This has the effect of concentrating pagerank only on the most important pages of the site and in some situations this is desirable.
Non Hierarchical linking is when all pages are linked to each other and are therefore considered of equal importance. Pagerank would therefore be distributed equally among all pages of the site therefore giving more pages a pagerank but of a lower score. While pagerank does not necessarily determine the page’s position on an SERP, it is something that customers may consider when evaluating the reputation of your site.
When performing internal site linking, you need to make sure that you use text links rather than image based or javscript based links. The anchor text should also contain the keyword relevant to that page. Large sites should incorporate a sitemap page from which all the main pages of your site can be accessed, and an xml sitemap from which all the pages of your site can be accessed.