If your site is hard to understand, unattractive, plays music that can't be turned off or riddled with flash that is distracting and slow loading, it won't matter how well optimized for search engine visits your site is, PEOPLE ARE GOING TO LEAVE! Human visitors are the number one priority.
This is currently one of the top search engine optimization targets for Page Ranking. Current research has shows that link popularity is a strong determiner in driving high site rankings. With reciprocal links being 10 times less important. These links can be internal, but external outbound links and especially one way in bound links.
Choose your links to and from the Internet very cautiously. If you are linked to sites under construction or low Page Ranking (PR) sites you get dinged by Google and your PR is affected.
Use keywords in the URL (Uniform Resource Locator) for effective search engine optimization. The core of a URL's is the domain name, which is your primary address on the web. Sites with the keywords in their URL usually rank highly and get special sub-links that display your blog, contact page or other special human interaction pages.