Alison Kent has an excellent post about the business of writing, priorities, and focus. She quotes Lee Goldberg on this and others. I agree with 99.99 percent of what they all say, with this proviso:
There will always be flukes. People who buy a lottery ticket for the first time and win 17.3 million; the guy who writes a really awful novel with a compelling plot and makes 17.3 million because he’s there with his awful book, right time right place. On the other hand, the woman who lives in the apartment downstairs (or the guy who lives upstairs) can follow all the best advice and write a great book and never make it.
There’s nothing remotely fair about this, but it is true.
A lot of this business is timing and opportunity. Persistence and dedication and craft are the things that will take you the farthest. My best advice:
You’ve got to have a good story to tell. Work on craft. Read widely. Work on craft. Work on craft. Take constructive criticism and work with it. And good luck.