Usually we'd start with a layout. That's how I like to write and rough out the details of a comic book story; in layout form. The layout isn't meant to look great, I don't really try to put the characters on model, or polish it at all. It's just to get a basic overview of the story. Here's the layout from a Charlie Hippo comic book from the early 1990's:
Mike takes the layouts, blows them up to the size of a standard comic page and pencils the artwork. Along the way, he refines the character poses and cleans up problems with the layout. The pencils are then inked and lettered to produce the finished page:
Ahh well, so much for comic nostalgia. I'm currently knee-deep in writing chores for our new book, but enjoying every minute. Back into seclusion I go!