What is the significance of keyword effectiveness index in search engine optimization ?

Is it right to select the keyword which has got high keyword effectiveness index for search engine optimization ?

It is important to know your keywords. If you have a product that you sell on your site, ask five friends what they might search for on google/yahoo to find it. Take those different keywords and optimize your page with them.
Also work on your meta tags. Here is an article on how they work: http://www.richkahmer.com/meta-tags.html