Use cliches. Introduce flat characters and improbable dialogue. Just write.
Make stupid mistakes and ignorant assumptions that you later kick yourself for. Don't show it to anyone; just write it. Write something so gratuitously self-indulgent and long-winded that you wouldn't force even your worst enemy to endure the whole thing. Then put it in a drawer for awhile -- a day, a week, six months -- and come back to it.
Sometimes you will surprise yourself and find that it wasn't as bad as you thought.