Here are some ways you may sabotage yourself:
1. You always put off writing until tomorrow, when you have more time, don't have a headache, have made up with your spouse, your computer stops making that weird grinding noise, you can get a whiteboard for your mind maps...
2. You judge your writing. There are two parts to writing - generation and organization. Only two. Don't judge. You're a lousy judge of your own work.
3. You don't follow up. An editor asks to see more of your work, and you think it's just a rejection, so why bother? Follow up, please.
4. You don't communicate. If no one knows you're a writer, how will you get readers?
5. You never finish a piece of writing. You start an article, novel or screenplay and never get beyond page 1. Complete it, whatever it is.
6. You think everyone else is a better writer than you are. They're not. If you're interested in writing, that's a sign that you can write WELL, with some experience and practice. Rotten writers aren't interested in writing or reading.
7. You want to become a freelance writer, but you never send out your work to people who could buy it, or -
8. You stop at the first rejection. When should you stop sending out your work? When they toss the first clod of earth on your coffin.
9. You listen to the advice of people who are not writers, AND you listen to the advice of people who are writers. You know your work. Chances are that if you've only written a draft, most of your work is still in your head. Take your own advice. Listen to your intuition. Who should you listen to? To people who are paying you - editors, or clients if you're copywriting.
10. You allow yourself to be ruled by your emotions: you have to be in the mood to write. News flash: you get in the mood by writing. The writing generates the "writing mood". Try it. Start writing at a time you're "not in the mood". You'll shock yourself - after ten minutes, you'll be in the writing flow.