Planning your animation before going at it makes it much more enjoyable. It's temting to just jump right in, but that's the worst thing you can do.
Thumbnail, Thumbnail, Thumbnail, get out of your chair, act it out, and thumbnail some more. Work small, I like to work small because you can get a lot of ideas down quickly and it forces you to think in silhouette. You can't draw that much detail small. The great thing about thumbnailing is that you don't have to be tethered to your desk to do it. Recently I was stuck in a long boring meeting, I took my sketchbook, instead of waisting an hour I felt like I was able to work on my shot for an hour. When I got back I knew exactly what I wanted to do. It saved a lot of time.
If you look on page 236 of Illusion of Life there's a great page of thumbnails that Mark Davis did. This is kinda like what I like to do (except my thumbnails don't look as good). I like to explore the idea firs, get a bunch of crude drawings down and don't think about the order of things. This is where I think about how a character would do something, like hold a glass, or open a door. This is also where I try and come up with the most entertaining way of doing an action. Then after I've come up with a dozen or so different ways of doing that one action, I video tape myself, so I can see the subtle things I might be doing without thinking about it. Then I'll go through the video tape and pick out the actions that work. Then I'll thumbnail again, this time I do things in order. I try and let the flow in at this point. This is where I do a lot of improv, I get the thumbnails down quickly only focusing on the forces and the action. After that do I launch Maya and pose out the characters.
Even in Maya I work in the lowest rez possible, shutting off anything I don't need. Get the poses down quickly, flipping between poses as best as I can.
I'm working on a 500 frame shot right now. So you better believe that I'm planning the hell out of it.