A great book called The Listening Book had this wonderful quote:
Restrictions will set you free
Someone says, "Write me a piece of music. Anything. No restrictions. Go!"
You're stumped. The blank page syndrome.
Instead, someone says, "Write me a piece of music using only a flute, saw, and this broken toy piano. You can only use the notes D, E, and B - but never all 3 at the same time. It has to be in 3/4 time, start quiet, get loud, then get quiet by the end. Go!"
Aha! Now you're cookin'!