I have a rough overview of how the story will go overall and how it'll end in vague notes and in my head.
Then I have notes and stuff about what each of the major storyarcs will be, typically comprising what makes up a "book".
Then when I'm getting closer to a storyarc, I start to write it out as bulletpoints of what needs to happen, and then a script, which I'll revise it over and over and cut things and stuff. The storybeats I have to hit are often big, soft targets, giving me a lot of room for different ways they could happen. So my targets in any first book will be things like "introduce each major character" and "Establish how they all got thrown into this situation" and "Have them score some kind of minor victory to cap off the book and bring them together as a team with a united goal", but how those things happen can be played with a lot.
Then comes the thumbnails, which for me is when the comic really takes shape. I have a much stronger idea of the pace of the story and how much space I'll have for dialogue when I draw out the pages in rough on paper. But even at this stage, I treat the wording only as a rough guideline. The exact wording doesn't go in until all the art is done, and can be heavily influenced by how a certain expression came out, or the shape of the speech bubble.
So I guess I'd call my way of making a comic kind of "iterative" or if you wanted to use an industry buzzword an "agile workflow". I have a plan for what I'm aiming for, but nothing is really set in stone until the pages are posted.