I don’t know if I’m the best person to ask, since I’m not successful by any stretch of the imagination, so take this advice with a grain of salt:
Work your ass off. Tons of people will be better than you—just make sure you’re the hardest working. Learn from those you respect and dissect what it is about their work that connects with you. Art is a terrible way to make money, so be prepared to have massive ups and downs. A lot more downs than ups, actually—for a long time. Every time you feel like quitting, ask yourself if it’s really what you want to be doing, and if the answer is “yes,” keep pushing. Be the last one standing. Over time, your skill and taste will continue to improve, though rarely at the same time. As best as I can tell, the secret to success is that there’s no secret. It’s a grind. That being said, value your work—don’t let people walk all over you. If you stick it out, people will begin to notice and appreciate what you do.