There are two ways of doing this (that I know of).
Pick a color as your border and as frames throughout. Then each square becomes one piece of the story. This can be as intricate a pattern as you wish to make it. It can be an abstract or actual characters or even words. Decide how big you want to make the quilt and then figure out how many squares you'll need to make and how big...then divide the "story" into each section.
Another way is to do a large "watercolor" style quilt where you actually paint a picture using fabric...it could be a collage.
I don't know what the traditional method would be but I've seen these two methods used very creatively and they turned out quite beautiful.