Develop a specialty. Once you've had one novel or nonfiction book published, you can present yourself as a professional when you try to sell your next book. If you pick the right subject or the kind of novel that lends itself to a series of books that you will enjoy writing and promoting, you can create your own brand and carve a career out of it. Also think of yourself as an infopreneur who makes a living by coming up with ideas and selling them in as many media as possible. Be passionate about your ideas and your books.
People thrive on passion.
If publishers believe in a book passionately, either because they love it, they think it will make money, or it simply must be published, they will publish it. Only write books that you are passionate about creating and promoting. You will know more and care more about your books than anyone else. But it's transmitting your passion and the passion that your books arouse in others that forges the links in the chain. Mobilize your networks.