1. Squash and stretch.
2. Hold keys.
4. Clear staging of action and narrative.
5. Realistic weight.
6. Smooth, natural motion arcs.
Be sure to check out Steve Hammond's Ball Story (above). It's a nice example of all of these things in action using the very same ball rig. Before you start animating, you must do a storyboard breakdown of the animation which includes all of the key poses and rough timings.Here are the demo videos demonstrating storyboarding, holds, and animating a simple jump with the ball rig.
If you want to get nuts with Lt. Dan. Here he is.