I'm working on CoffeeParty's second dojin book, In Search of Lost Coffee. We - Saeko Doyle and I are making the storyboard now, it's our collaboration.
We just decided basic ideas, characters, the start, so on - then draw the storyboard (2 open pages) one after the other. First 2 pages were done by Saeko, and I did the next 2 pages, then pass it back to Saeko.
You don't know how the next 2pages will go when you passed your part. And when you take the back, you make the sequel. You accept the story you get, no touch, no interfere each other, you enjoy the surprise and struggle with it to get the next 2pages.
This is one of the storyboard, I think I can show the manga-style storyboard (コマ割) with this. It can give you a glimpse of how manga stream is oriented
The "wide gap" between panel 1 and 2 of 2nd page, it shows the place/time was different. It's supposed to work like a wipe in film. This is very common - classical technique of manga.