Great animators take pride in asserting that "there are only 3 things in Animation":

Anticipation
Action
Reaction

When you are facing a certain animation is important to get somebody to act it out, re-create the scene if possible, get reference footage, or take the time to go to a place where you can observe it in real life. You need to analyze the real motion and divided in important steps, that you will later reconstruct with keyframes.

When you animate, you Re-present (present again) a real movement of a combination of real movements. To create an impacting animation, you need to understand how the animation process modifies a real movement to better represent it.

See how we use the anticipation of a movement as a necessary step in a full motion animation.

The 3D animation belongs to the site:
http://www.comet-cartoons.com

Scroll down the page:
_Animation and Setup tutorials / Character Animation: Principles and Practice