My initial plan was to take some kind of simple geometry, and then carefully plan my values to make it look good just by lighting. But, there was so much about the piece that kept bothering me that I never got to that point. I guess I can't really skip thinking about composition and forms before lighting.

I did realise something interesting though: the higher contrast you have between light and shadow, the less forgiving the image gets towards flat values. That's the theory anyways.