Problem: You have no freaking idea what to write, to play, to paint. The canvas or page is an ocean of white nothingness, and it’s frightening, frankly.
So it’s time to change scale. Whatever surface—or time period, to relate it to music—you’ve got, put it aside and get something much smaller. An index card, Post-It Note, a single mono track. Use one tool, one color, one instrument. You can fill that space a lot easier than a big one, and break the starting barrier, the hardest part of creating.
Once you feel yourself starting to drop into the flow/zone/zen, you can generate an idea or three and move back to a larger space when you’re finished. Or before, if the spark is there.