I'm an extremely visual thinker, my ideas for scenes are usually detailed enough in my head that I can essentially play them as a mental film. When it comes to translating it into physical media, I start off with a rough storyboard of what I see and at the same time I decide the panel layout as I'm sketching. During this time, I fiddle with the characters' poses, angles, and blocking. My biggest weakness with this strategy is that my "mental film" doesn't include speech bubbles, I hear everything my characters are saying, so when it comes to deciding where the text goes I have to start adjusting the scenes even more (I often get a really satisfying aesthetic for a panel, then realize I left no room for dialogue).
Anyway, once all the storyboarding is out of the way, I fill in details and that's where most of the honing of my character designs comes in (if I haven't already used the characters before). I usually already have a rough idea of what the characters look like, but when I see it drawn out I might reconsider certain things, so I'll redraw or redesign some details during this process. Sometimes this will happen even if it's a character I've made reference materials for - I'll realize some aspects of their design might look cool if they're just standing around, but making their poses more dynamic could trip me up.
Dialogue is usually the last thing I settle on - the more I reread or rethink what the characters are saying, the more I feel like it should be altered a bit. So with my storyboards, I'll have a pretty solid idea of what they're saying, sometimes I'll even write it out in the draft, but by the end there will be a number of changes.
Every now and then, the final step is to look at my completed work, decide it didn't turn out as I had hoped, and redo it from scratch (luckily, this has only happened with my simpler pages).