As the Nike ad says, "Just Do It"

Park your ass in front of your computer, typewriter or paper pad and pen and just let your ideas flow.

Don't edit yourself, just get it all out as fast as you can.

Then sit on it for awhile. Then go back and polish it up. And maybe even re-polish it again. Whatever it takes.

Repeat process again and again and again. Allow yourself to write crappy stuff. Do this enough, and some of it will turn out pretty darn well.

Good luck to y'all.