Search Engine Optimization results depend on good keywords. so we need to give good keywords which are more frequently searched by users. some times it is difficult to bring top rank to your site with most popular key words. then you need to give the key word more specific either geographic or sector specific. ex: “jobs” is a most popular key word so give ” jobs india” or “jobs software” then we can get our site top rank .
Some free tools are available online to find best keywords. http://www.google.com/webhp?complete=1&hl=en