Never mind my advice; listen instead to Robert A. Heinlein. His advice was simple:
1. You must write. 2. You must finish what you write. (2.5 You must revise what you write.) 3. You must market your writing. 4. You must keep it on the market until sold.
He didn't include much about revision, but to me, that's the key: all the best writing is rewriting. That's when you cut out the fat, sharpen the descriptions and jokes and everything else, and make the manuscript really sing.
But you can't do that unless you first write, first finish what you write, and then see what you've got. After that, you just have to try and try and try again. There really are no "overnight successes" in the world of writing. Most every writer will tell stories about learning her craft by writing story after story and just doggedly sending it round until finally someone said, Yes! This is terrific!