Two artifacts from the same episode prep.
I usually start by drawing characters or locations, almost to kill the time while I wait for loose ideas to consolidate into something concrete. Scribble down some big beats, a few fun visuals, just the hits please.
Later I'll start a text document with bulleted entries on locations and characters. I think of games in cinematic terms, so often I'll list the details that a camera shot might highlight, and trust myself to wing everything else.
If past Andy was good to future Andy, this document will include reminders about how to manage the mechanics of challenges or combat that might emerge in scenes — for example, since we're playing Forged in the Dark, a list of clocks I might set. But the weakest part of my GM approach is managing mechanics, and often I struggle in the moment to root my plot and character development in the game rules.