Here are a few doodles from my current s-l-o-w-l-y progressing sketchbook. I worked up the values in photoshop...

I find that drawing in low light can really help make for a more interesting drawing. Often if I'm drawing while watching TV, the lights in the room are pretty dim, and it keeps the sketching loose and very fast. It can be a nice exercise to help disengage your brain when you are thinking about things too much. The guy in the lower left hand corner could be Darth Maul's pudgy, out-of-shape, underachieving older brother.