Xeroxing your artwork.  This is a trick I used for a recent set of graduated illustrations.  It's very simple to do and allows greater continuity of design, as opposed to redrawing each illustration from scratch.  In my case I wanted to have a graduated set of  images that eventually became a Gothic window.  The final image was based on an actual church window in England.  I started with the basic elements...a square set with a vertical and horizontal line.  This I saved as Image #1.  Then I copied it and added a few more details.  Voila...Image #2.  I added even more detail and had Image #3...and on I went  As I progressed I gradually started taking away inside lines, curves, and so on, and my finished window image began to look like the real thing.  Each image was then placed on the chapter pages of my book, giving the reader the impression of looking over the architect's shoulder as the image was being designed.   Not too shabby for an architect wanna be!