Robert A. Heinlein, the famous Science Fiction writer, always maintained that there are 5 rules for writing success.
1. You must write.
2. Finish what you start
3. Don't rewrite, except when an editor tells you to
4. You must put your story on the market
5. You must keep the story on the market until it sells
Science Fiction Writer, Robert J. Sawyer lists these rules on his blog, On Writing, and adds another rule of his own -- 6. Start working on something else.
He explains these rules in detail, plus points out why, out of 100 would-be-successful writers, only one will be successful. (for example, out of 100 writers, only 50 will actually write. And less and less end up following the remaining rules to success.)
Click on over to read his blog.