Best way is to just start. Even if you feel the output is useless gibberish, and just keep at it for at least short time, maybe 15-30 min if you can. Then take a break and revise the gibberish, you’ll be surprised there will be useful starting points in there, or you’ll think this is all wrong, it should be xyz instead- and there you have it, you’ve started and have a direction to go in.