Okay, I think the best way to learn is to jump in and try. So how about a challenge. Pick a subject you really love and choose about a dozen images. (you need to have more than you need to pick from). I usually start with the size that I need the end result to be in the design.
Lets take about a couple weeks and see what we come up with. Then post and critique. Lets say a 16x20 image as the final. Who's up for it? How about putting images up on election day?