I like to write my whole script out like it was a scene in a play, with minimal descriptions (like so)
Character one: I'm starving
Character two: me too.
they walk into the darkened kitchen
and then I don't worry about where the panels or page breaks are going to be until I'm totally done, and figure out how each page is formatted when I do thumbnails. Depending on how complicated the scene is I'll do three or four rounds of thumbnails working out how the scene is going to play out. I find that it gives me more freedom in the writing, since I can just focus on the scene instead of the art, and then when you are doing the art you can play as much as you like. Remember that the size and numbers and even shapes of panels in comics does a lot to set the pacing, the tone, what moments stand out, etc. So you want to give it as many trys as you need to get it perfect.
Another thing I've found helpful, especially in 'show don't tell' stories where the dialogue isn't as important, is to get as creative as you want with the action directions. Even if no one will see them but you, it's good to give yourself as much detail as possible to work off of when it's time to draw. Say your script says this:
she takes his hand. he waits a moment, then squeezes hers back gently
it's fine, and you could definitely make some nice comic panels out of that. But if you did something like:
she takes his hand. he doesn't know what to do for a second, he's been dreaming about a moment like this for so long, and now he's at a loss for words. Instead of saying anything, he just squeezes her hand back gently, hoping she can feel his affection through her glove.
pretty cliched example, but even though that would only translate to two or three panels at most, there's a lot more to work with, so if you're going back to an older script or even if you're writing for another artist, the art can work to reflect all of that. I would recommend reading other comic scripts to see how the writing is translated into comics, and maybe some movie scripts as well. They're more widely available, and a lot of the same tricks for writing action line apply to comics. There's a lot of youtube channels like Lessons From A Screenplay that break down movie scripts, and which have a lot of tips that are also helpful for comics.
Anyway, that's about all the script advice I have. Obviously, you don't have to take any of it, and not all of these techniques will work for everyone, but hopeful at least some of it is helpful? You're already on a great path so far. Good Luck!