This sketch above is from Dan Roam’s book, Back of the Napkin, a book about solving business problems with pictures. He has a system that matches six ways of seeing with six ways of showing. Could this be a basic framework for approaching and sketching out design challenges?
Comic style sketch
Prototypes are used to tell stories. How you tell a story greatly defines what you tell. Matt Madden has an excellent book and site dedicated to this subject with 99 explorations of the same story through variations of stlye. The various forms inform us in different ways through style. One of my favorite examples shown on his site is the same story from the image above only in the form of a map.
For more about illustrating and writing in the comic style, see the work of Scott McCloud.
Map view
An excellent example of how prototyping works from idea to production. Observation > Sketching > Modeling > Testing > Revising > Specification > Production. One of the interesting things to watch for here is the level of fidelity in the methods. Sketches, models and prototypes all advance the concept and feed back into its refinement.