During my senior year at SCAD, I had the great opportunity to take a class under Glenn Vilppu, on Classical Composition. At the time I was a little disappointed that I couldn't get into his Figure Drawing class, since that's what he's most known for, but more and more I'm so grateful that it was the composition class that I took. Hopefully at some point I can upload a pdf of my class notes, but you can go to AWN (or look for Vilppu's name in my links) and check out some of his general lessons there.
He spent almost every class analyzing some classical painting by drawing lines over top of them in photoshop (or painter or something). He talked about things like using opposites, shapes, and the flow and rhythm of a composition--as opposed to just framing. He always said that he used these principles to compose his figures too, though I didn't really understand how. Now when I study classic Disney animation and even films like The Little Mermaid I see these principles of composition in the poses all the time! My main goal in improving my skills right now is to try to really compose the characters well, with good use of negative space and movement in the pose.
I don't have time to post about it all now, but I wanted to post a link to John Kricfalusi's blog.
John is the creator of Ren and Stimpy, and although I don't share his taste for over the top Clampett style, he is posting some very informative lessons on bringing artistic principles into animation. He has a whole category of posts dedicated to composition, mostly in terms of backgrounds, but as Vilppu said, you can completely apply these to drawing characters in poses. John is pretty negative about the state of animation today, and while he makes very good points I don't quite agree with all of them. He also explains the principles of composition in different terms (I think I still prefer Vilppu's way of teaching), but regardless the ideas are the same.
John's posts on composition
The more I think about, contrasting poses, flow, rhythm and other elements of composition, the more I see that even a lot of great CG animation doesn't have it--mine included. I'm feeling more and more that these elements really push animation to a more entertaining and appealing level, and everything else really falls short of its potential, and just becomes natural movement with good timing. And the thing is, a lot of our principles of animation and design are actually based on composition, but those aren't the terms we think in.
Man...I told myself this would be 'short'. More on this later.