Search engine optimization (SEO) is the art of getting a website to work optimally with search engines like Google, Yahoo and MSN. Search engines find your site by other sites linking to it. Google spiders this link, finds your site, and indexes the home page of your site.
Search engines are the key to finding specific information on the vast expanse of the World Wide Web. Without sophisticated search engines, it would be virtually impossible to locate anything on the Web without knowing a specific URL
There are no hard and fast rules to SEO, other than developing quality websites with quality content and quality links pointing to it. SEO helps to ensure that a site is accessible to a search engine and improves the chances that the site will be found by the search engine.
If you are thinking about hiring an SEO, the earlier the better. A great time to hire is when you're considering a site redesign, or planning to launch a new site. That way, you and your SEO can ensure that your site is designed to be search engine-friendly from the bottom up. However, a good SEO can also help improve an existing site.