Peter Mayle, the author of A Year in Provence, says "The best advice on writing I've ever received is from Henry Miller's On Writing: You have to write a million words before you find your voice as a writer."
This scares new writers, and I'm not sure why. The only conceivable reason to aim at a professional writing career is because you want to write. Writing is the job description for a writer, and the more of it you do, the better at it you will get. If you doubt this, go and find something you wrote twelve months ago. It may make you cringe. Even if it doesn't, you'll find ways to write it better now, because you've had more writing experience.
So write. :-)