I attempted the contour drawing excersise today to see how I would fare.
There are a few things that I would do differently.
I set up a simple still life with a desk lamp lighting it from the back. There was a bit too much ambient life to emphasize the shadows dramatically enough, a stronger light would have been better.
Marking a border inside the edges of the page was helpful. I sketched the basic shape of my objects and the shape of their shadows, but instead of refining the various shadow and highlight areas with more contour lines, I started filling in the shadow areas from the lightest to the darkest.
I used my eraser extensively to get rid of unwanted lines and I also used it to smudge the pencil and create a smoother texture. Later as I went darker with my B6 pencil, I erased the lightest areas to make sure that they were not smudged over. I spent about one hour on the drawing.
It was a good excersise and one I will try again!