When writing story based comics, I need to do a script of some sort otherwise it always feels like it's lacking a decent foundation lol. My improv work isn't very strong, imo.
That said I'm sooooo slow at it and find it harder to focus on sitting down and writing them than actually drawing the comic, but it's a necessary step for me so I grin and bear it!
I start with this (this part usually goes quickly), but then after that I go back in and write several paragraphs in more detail under each plot point about what exactly happens. it's similar to a rough draft for a novel, but looser because I can make notes to myself and stuff mid-paragraph since no one will see this anyways.
I also don't spend a long time sussing out very much dialogue or panel-by-panel action at this phase. I prefer to do that sort of stuff when I get to the storyboarding phase. I WILL make note of specific dialogue lines that come to me or are important to be worded a specific way though, as well as any really specific expressions or poses. It's basically a manual to future me to get things the way I want them in the story board.
Then after it's all written out... I try to do a few editing passes, change stuff, smooth rough or awkward parts out, etc. Part of this process is me also trying to guesstimate how many pages each scene will take, and I like to have a rough target of total pages to keep the project scope in check, and then if the estimated amount of pages is like... way more than I was hoping for, I go through again and try to cut/shorten different parts until I'm in the ballpark. Like, I don't technically have to do that since on a digital platform I have as many pages as I want, theoretically. But I find imposing some limits like this helps me to keep the story concise and focused which can help the pacing and also shorten my workload to a reasonable amount.
After that's all in check I'm ready for the story boards~