I missed SuperScrounge's earlier comments about comic scripting. Even though it's late I want to respond. When I was pencilling professionally I worked on only one fully-scripted story, an 8-pager. The script was laid out the way SS does it: each panel described by a short paragraph followed by the dialogue.
All the rest of the work I did was for Roy Thomas, who used his personal flavor of the Marvel Method. Roy sent me a 6-8 page synopsis describing the action with notes about possible dialogue. He broke the synopsis into sections, e.g. "Pages 1-6," "Pages 6-14," etc. Each section consisted of several brief paragraphs along these lines (I made this up off the top of my head; don't blame Roy):
Star Spangled Kid tries to convince Jonni to stay. Garzok too powerful for someone without super powers, let me take him on. Jonni says no, I promised Dad I'd bring Garzok in and I'm going to do it. She pushes past SSK, jumps through window. We stay inside with SSK: he hears explosion outside. Jonni cries out.
I was always impressed by Roy's sense of pacing. No matter how I laid a story out, each section always ran just as many pages as he said it would and the story proceeded smoothly from start to finish. Guess it's a knack you develop when you've written thousands of comics pages.
I sent the pencils to Roy and he wrote final dialogue. If I had a particular idea I'd jot it in the margin. Once in a while Roy'd pick up on it, but he always had a clear picture in advance of what he wanted to say. 99.9999% of the dialogue was his. One of the delights of working was Roy was the way he could tweak a scene with an unexpected line. There's a scene in Alter Ego #1 in which the Green Sorceress vamps AE into removing his mask. Roy's tongue-in-cheek dialogue still makes me smile.
Anyway, Roy made a copy of the page and drew circles indicating where balloons would go. Each circle was numbered 1,2,3, etc., keyed to the dialogue pages. These went to the letterer. Roy was a whiz at locating balloons so that dialogue read properly without covering important art. It's a harder job it seems. I know from experience.