Aaron Yamada-Hanff, a coworker and friend of mine teaches concept art, and he told me about an exercise that he has his students perform. In this exercise, he has the students look at something they're interested in or otherwise relates to things they like drawing for about 10 seconds. Then, they put the image away, and are instructed to copy it.
The exercise is meant to broaden your memory and observational skills, while simultaneously forcing you to make design decisions. Its a very cool exercise, one I wish I had been doing a while ago.
This is my first foray into it, and I'm cautiously excited. As you can see what I drew and what was looked at was wildly different. Very, very nacho.