The following is from GOOGLE. So consider the source.
SEO is an acronym for "search engine optimization" or "search engine optimizer." Deciding to hire an SEO is a big decision that can potentially improve your site and save time, but you can also risk damage to your site and reputation. Make sure to research the potential advantages as well as the damage that an irresponsible SEO can do to your site. Many SEOs and other agencies and consultants provide useful services for website owners, including:
Keep in mind that the Google search results page includes organic search results and often paid advertisement (denoted as "Ads" or "Sponsored") as well. Advertising with Google won't have any effect on your site's presence in our search results. Google never accepts money to include or rank sites in our search results, and it costs nothing to appear in our organic search results. Free resources such as Webmaster Tools, the official Webmaster Central blog, and our discussion forum can provide you with a great deal of information about how to optimize your site for organic search.
Before beginning your search for an SEO, it's a great idea to become an educated consumer and get familiar with how search engines work. We recommend starting here:
Some useful questions to ask your Developer/Designer about SEO include: