SEO is a very integral part of any website. I would advise hiring an experienced SEO consultant or company to assist you with the SEO of your site, as if done incorrectly can actually have a very negative effect on the site and even get you removed from the search results pages on the likes of Google or Bing.

There is software out there to assist you with SEO and some of it is free, but you must be careful when using any of this software as some of it is not up to date with current SEO rules and recommendations. Certain programs allow you to enter a particular keyword and analyse other websites that are ranking for that phrase and show you what links, keyword density etc they have. Again this can really help but should be looked over by an SEO consultant to show you which elements are important and which you should concentrate your efforts on to get the best result.