I usually divide my story into segments or arcs. So before I start writing/publishing them, I have the whole rough drafts done. Yes, it's novel but I think it's still related to the questions 
As for comic, I would try to avoid it until I have finished at least 70% of the story. I mean, yes... I've never even published one or even have the skill to publish one but really, the thought of making the story into a comic never crossed my mind until I know the story would be ending soon.
Recently, I found an artist that would offer me collab and I have just learned scriptwriting for future use. Though they say they won't be able to start until after August, I thought I'll get an early start on the script. I've tried writing the script without reference first because I remember my story from A-Z, and found it alright, but it was much easier when I referenced my own already written chapter.
In short... for a novel, I plan one arc before I start writing and publishing them, and for comic, won't start until the story is 70% done.