You have a big job ahead of you. A good overview of what you must do is chapters 21-23 of The Complete Idiot's Guide to Getting Published. Or go to the bookstore and look in the reference shelves for those books on "How to be a writer," and find the books on book marketing and self-promotion. Buy one (they give pretty much all the same advice), read it and do what it says.
Before selling you must determine whom you want to sell to and how to reach that segment of the population. You will be writing press releases, making phone calls to media and organizations, and making lots of personal appearances. If your book is fiction it will be much, much harder to sell than nonfiction. Please do not embarrass yourself by going to chain bookstores asking them to carry your self-published book. They will not; dozens of self-published authors approach them every week. The majority of your sales will not come from bookstores anyway but from personal appearances which you must set up.