Keri Smith, to whom I referred a few posts ago for her list of how to infuse your work with your personality, also has a list of point about how to get published. Three of them relate to selling your work:
* Make it real. I borrowed this one from Sark, but I read it years ago and followed through with my first book (which I sold). I made the book in its entirety, packaged it up really smartly in a box with fake hay so when they opened it, it was somewhat displayed. This shows the viewer exactly what you had in mind, without them having to visualize it. Invariably if you explain something, they won't see exactly what you are thinking. anecdote: When I met Sark in person a few years ago and told her I got a deal with Chronicle she jumped out of her chair and screamed, "I'm so JEALOUS!!! (This suggestion is appropriate for people who wish to write AND illustrate. I do not recommend having someone else illustrate a book before you submit to a publisher as I have been told by many editors that this will actually hinder your chances of getting published. Do it if you can execute it in a way that is flattering.)
* Research and target the appropriate publishers. This is extremely important, really look at their newest catalogues. Would you work be an appropriate fit? Are they using people with a style that is compatible with yours? I'm not saying to cater your work to them necessarily, but find an appropriate fit for you. I read the Writers Market like a novel, and used a highlighter throughout. This gives you a good indication of what certain publishers are looking for and how to present your work. One of the most common mistakes that authors make when submitting work (according to editors) is submitting work that is not suitable to their list. This ensures that you get your stuff into the slush pile.
*recommended reading "Writer's Market", or "Writer's Guide to Book Editors, Publishers and Literary Agents" both published yearly.
* Really sell yourself to them. Put together a package with a bio, list of clients, testimonials from clients, target market for your piece, and a sales pitch (as in a press release) about why you created the book and how it might be presented to the public. Also I always mention that this is not a simultaneous submission in my cover letter, (this is common courtesy in the publishing field), and that I purposely chose _________ because I felt the work would fit well with their list, in concept and visually.
*recommended reading "Six Steps to Free Publicity" by Marcia Yudkin
JW note: I think this common courtesy (of not submitting to more than one publisher at a time) would be fine if publishers responded quickly but they can take months and months, so if you go one by one you could spend years before someone accepts your work. Sometimes I do submit exclusively to one publisher, but generally I advise submitting to several unless they specifically say in their writers' guidelines that they will consider only exclusive submissions. In that case, if you don't get any response within a reasonable time, let them know you're moving on, and submit to others. Frankly, the deck is stacked too much in their favor for us to play the game only as they want it.
Keri's full list is here, and you may also want to check out some of her books, which are all about creativity and art.