For me personally (specifically referring to Palette Swap), I come up with a decent amount of ideas ahead of time and also kind of progress at a slow pace relative to that since the story arcs usually are split across multiple issues. I think it also helps that I have pre-existing framework to work with (mafia games and other community events) that makes coming up with ideas easier, plus I also work with Magolor on them and we bounce ideas off of each other from time to time.