For Kamikaze, a very long form comic, I tend to write out the ENTIRE 'episode' of each installment before we even get started drawing. I come from a screenwritng background, so the idea of writing with no idea of where the heck I'm headed is a great way to turn me into a puddle of anxiety.
So I have an entire arc written out, with the very, very basic stuff laid in place. I've broken down the series into around 7 'seasons' of 13 stories, or as I call them 'episodes'. Each episode is 5 acts - 0 throught 4.
Each episode is beaten (screen writing term for figuring out the plot mechanics of important points) out and then separated into acts. From there I flesh out each beat with a more detailed description of what happens. Then the the beats are grouped together into scenes and separated into acts. Finally I start writing, skipping around to what I reeeeeally want to write first. This is the cool thing about planning stuff out: You can skip around and still have things in order! That action scene you're dreading writing? SCREW IT! Write a different scene! It's so liberating!
For anyone doing long form comics I REALLY suggest doing live read-throughs with people who don't know the story. Your writing, especially dialogue, will be much, much better for it.
The way I do it is a slow process, but when you're writing 30 to 45 pages of comic, you've GOT to have a plan.
TL;DR - I'm insane and write 30 to 75 page comic scripts all at once, before putting pencil to page. Then I edit, and DO IT ALL OVER AGAIN.
Accurate picture of me writing:
