Harlan Ellison once offered the following advice to aspiring writers:
"I must've lectured at 3,000 universities, all over the world, including the London School of Economics, and Yale and Harvard. Invariably at every single public presentation someone will come up to me the way Willy Loman asked his brother Ben in Death of a Salesman, "Ben, Ben what’s the secret? What’s the secret?" and Ben would say "Diamonds, Willy. Diamonds." Well, they come up and ask me, "What’s the secret of success? How do you make something of yourself?" And I give them the secret. There is only one secret, and the secret is this: Anybody can become a writer. If you look at bad writers like Gregory Feeley or Judith Krantz or John Grisham, and you look at the crap that they write, you realize that things that live in a petri dish, for christsake, can become a writer. The trick is not becoming a writer. The trick is staying a writer. Day after month after year after story after book. That's the secret. And if you can do that and produce a body of work, no matter how large or small it is, that is true and can pull the plow, then you're a writer. If you are not prepared to spend your life doing that, then, for christsake, don't do it."
Lawrence Watt Evans has a wealth of knowledge on the subject of writing here.