Readings
It will help if you read the articles below in order.
"Understanding the search demand curve is critical, because it stresses the importance of "long-tail" targeted content - pages with information not directed at any particular single, popular query, but rather simply exposing the myriad of human thought, research, and opinion to the spiders of the search engines. As an example, below I've copied a chart of SEOmoz's own keyword traffic, illustrating the small number of queries sending larger amounts of traffic alongside the plethora of rarely-searched terms and phrases that bring the bulk of our search referrals:"
Tools