If you have decided to go the traditional publishing route, an agent is a very useful person to have on your side. To get an agent, you need a query letter, that thing that says pretty please, will you read my story.
Agents go through oodles of query letters a day. You want yours to stand out, but in the proper way. A good place to figure out how to do this is to check out Query Shark, a blog hosted by literary agent Janet Reid of Fine Print Literary Management. The archive includes years worth of critiques.
May the Muse be with you,