There's a great article by Jon Bell at Medium about how he habitually suggests the universally-hated McDonalds for lunch to indecisive co-workers—a form of "shitty first draft" (to quote the novelist Anne Lamott) designed to motivate others into actively suggesting other places to eat. The idea is to stop overthinking things and give people somewhere—anywhere—to start brainstorming, no matter how dumb that first idea may be.
Jon also advocates getting away from the computer:
"Not sure how to start? Sketch a few shapes, then label them. Say, “This is probably crazy, but what if we.…” and try to make your sketch fit the problem you’re trying to solve. Like a magic spell, the moment you put the stuff on the board, something incredible will happen. The room will see your ideas, will offer their own, will revise your thinking, and by the end of 15 minutes, 30 minutes, an hour, you’ll have made progress."
The same magic happens when you write in a notebook, away from the all-powerful formality of computer interfaces. Just dive in. Write it down, scratch it off, and worry about sorting out the good stuff later. The key is to just get started.