Urban Sketchers, I've wanted to read more about seeing and observation in drawing. In Bert Dodson's popular book Keys to Drawing, one of the first subjects he tackles is seeing vs. knowing. While knowledge of what an object looks like is helpful in general, sometimes we end up relying too much on our preconceived notions rather than capturing what we actually see. The key here is to enlist more curiosity, less assumption.
The above sketch is one of the first exercises in the book. Looking at your hand in an unusual position is supposed to force you to draw something in a way that comes out unexpectedly. I'm not sure how successful I was, but at least it's practice.