I do concept art of characters just because it speeds up the process a whole lot when I'm not inventing stuff of the cuff, so even minor recurring characters have some rough concept art sheets. Most of them look something like this:


With a couple vague place concepts that I built in blender once I had the vibe;

Then there's the writing process which gets at least 3 passes (scene overview, theatre-style scene writing and finally written storyboard where the script is cut into pages and panels) and then my drawn storyboard. I sort of need that amount of prep work so that I can go fast once I'm actually doing the pages.