This is the process I went through when I designed some of the characters from the story "Taste" by Roald Dahl.
First I made a lot of black silhouettes to find some random shapes.

When I found the shapes I wanted to use, I tried to convert them into head shapes

To find a suitable body I cut out some random shapes in Photoshop and played around with them until I found the shape I liked

When the size and shape of him was in place, I sketched, cleaned up and colored him. This is the final design. He is intented to be in a 3D animated movie. If I can find the time some day I'll model him in Maya and maybe make him in clay

It has been a great experience to try so many approaches to find the design that I wanted and that suited the story.
Thanks to Julia for a great week.
Here he is in clay