Write, write, write. Then write some more. Find a writing or critique group. Get feedback on your work. Take it seriously (but not TOO seriously). Stay true to your vision. Develop a thick skin. Edit, edit, edit. Oh, and did I mention WRITE, WRITE, and WRITE?
Apart from that, these days you'll have to learn about the business of writing. Find some trustworthy online sources (Jane Friedman and Joel Friedlander (The Book Designer) are two that come to mind.
Then write some more. And be very patient. I wrote for 30 years before I got published.