Of all the metrics used to determine the rank of a site there is one that underpins the power of search engines and was the foundation for Google's early success. This is the idea of evaluating the rank of a site based on which other sites link to it and the quality of those links. Google's trademarked term for this is "PageRank" however all serious search engines use this idea in some form today. It is a concept well worth being familiar with as it is still the single most important factor in determining the ranking of a site within search results.

Getting good quality links to your site is still the best way of improving the ranking of your site. And like many things in life it is "quality" not "quantity" that counts. Determining the quality of a link is itself a complex algorithm unique to each of the search engines. However as a general guide a "quality" link is one coming from an external site that has a high ranking itself, and has content that is similar or related to the site.