While no one can agree on just how important PageRank is to your overall search engine rankings, it is pretty certain that the number is a good indicator of the quality of your Web site. If you're looking to increase your PageRank, there's nothing you can do to get inbound links besides ask other people, but you have complete control over your site's internal links.
Internal links can contribute to a higher PageRank of a Web site. Google sees links as recommendations. It gives higher importance to external links (other Web pages linking to yours) but also takes into consideration internal links. Internal links tell the search engine which pages are considered important by you as a Web site owner.
Use Internal Links Wisely
Distribute PageRank. Your home page probably has the most external links pointing to it, and thereby has the highest PageRank. The pages you link to directly from your home page will probably have second highest, and so on.
Your Web site needs to have clear hierarchy and you need to know which pages should be emphasized. Some pages will get PageRank before others, depending on external links and content quality. Use your internal links to distribute PageRank from highly ranked pages to others. Here's a great blog post on how deep links help distribute PageRank.
Pay Attention to Your Keywords. The words you use to link from one page to another will affect which keywords the target page ranks for. So don't link the words "Click here." Turn your keyword into a direct link to the appropriate page.
Lower Your Bounce Rate. Internal links are also useful in decreasing your bounce rate. Your bounce rate is the percentage of visitors that examines one page and then leaves your Web site. Having adequate internal links will get Web site visitors interested and exploring your content in detail.
Remember to select internal link structure carefully. It should be used to emphasize your important content and to distribute PageRank from highly ranked pages to others. Last but not least, internal links should be user-friendly and should add value to the experience of Web site visitors.