Actually, I don't know.
But I was listening to a TED talk the other day on what makes a successful person, and I reckon what makes a published writer is pretty much the same 8 things as that speaker mentioned:
1. PASSION - don't do it for money, but for love
2. WORK hard, but let it be fun. (For a writer, that would include reading A LOT)
3. GOOD - get good at it through practice
4. FOCUS - on one thing
5. PUSH yourself and push through the self-doubt
6. SERVE something of value to others
7. Get IDEAS - listen, observe, be curious, ask questions, problem solve, make connections
8. PERSISTENCE through the CRAP Criticism Rejection Arseholes (or assholes if you're an American) Pressure
And honestly, I don't think you can get better advice on How To Be a Published Writer than the above. I might question No.4 (for a writer, too much focus on just writing might be too socially limiting for a start), but apart from that, I reckon it's damn good advice. It certainly applies to how I went about it...
What makes a successful published writer is something else again, and no one knows the answer to that one. If they did, there would never be a book that fails to sell well.