Certainly living life more fully and maturing enough to be able to reveal myself helped. I don't know any consistently successful novelist who doesn't have a good work ethic. Work, work, work. Write, write, write. And don't take yourself too seriously.
Writing is a great job, but in the scheme of things it's pretty trivial.
Any surgeon, dentist, psychologist, police officer, does more important work every day. The books that taught me the most about writing are the books I most admire, and I keep them within arm's reach of my desk so I can reread them whenever I need to be reminded how they did it. These aren't books about writing, but I find them more instructive than those sort of books because I'm the sort of person who learns by example. I liked John Gardner's how-to book, one by Jack Bickham, and also Annie Lamott's Bird by Bird. But I agree with King that the really, really best thing for a fiction writer to do is read novels.