The secret of becoming a writer is that you have to write. You have to write a lot. You also have to finish what you write, even though no one wants it yet. If you don't learn to finish your work, no one will ever want to see it. The biggest mistake new writers make is carrying around copies of unfinished work to inflict on their friends.
I am sure it has been done with less, but you should be prepared to write and throw away a million words of finished material. By finished, I mean completed, done, ready to submit, and written as well as you know how at the time you wrote it. You may be ashamed of it later, but that's another story.
Jerry Pournelle, How To Get My Job