If you want to appear in your site listing top search pages, you need to find out the keywords that are most relevant to your site. Apart from your imagination, there are three ways to figure out keywords.

Go to a search engine and perform a search for Web pages that cover specialized same as yours or perform a search on the condition that you think people will use to visit your site.  This is the easiest way, which you will find many of the most important keywords.

This exposes the whole HTML used on the site, including all keywords. Some of these keywords that will be relevant to your site. Make a list of these keywords. Now visit the Web site and learn more.

In 2.0 blogging and web sites, the keywords called tags. Blogs will display the list on the label or in the sidebar blog posts.

You may find the competition for a keyword in terms of the bidding price and the number of searches on Google Adwords and Yahoo.   Pay per click different locations, enabling you to see popularity of a keyword. Here is a link to the Yahoo tool, which is quite famous among the advertisers.