Squash and stretch

Makes animated objects like clay. A ball hitting a wall gets taller and narrower as it flattens on the wall momentarily, and then resumes its original shape. This punches up the motion and gives the viewer clues about the weight and rigidity of an object or character.

Anticipation and follow through

Animation is like throwing a ball. You must have a wind up, a pitch, and a follow through to make the action work. You need to build up to an action, and show the results. Anticipation clues the audience that something is going to happen. When Wile E Coyote goes off a cliff when chasing the Roadrunner, he pauses in mid air before falling into a deep canyon, then he falls and then you get a little dust cloud to tell you that he landed.

Staging

How is the action framed by the camera and what part of the area is used? You want to present the action in the clearest and most dynamic manner.

Slow in and slow out

Similar to a drag racing car accelerating or an F1 car stopping in the pits. The rate of motion changes for emphasis and adds to the subtlety that you can express.

Arcs

Arcing motion and curvy lines can be more attractive and powerful.

Secondary action

Motions driven by other motions, like Wally B's floating feet, can add a lot of realism.

Timing

The use of time in animation will affect pacing, characters, and the effect of an action.

Exaggeration

Exaggerating things makes it more interesting and accentuates the things you want to be most important.

Appeal

A character does not need to be as cute as Hello Kitty to have appeal, but the audience must have a way to relate to them and enjoy them. An object should also have appeal, pleasing proportions, and perhaps some sparkle to catch the eye.

Misdirection

Can be used to change the plot, or guide the viewer's eyes magician-like, so that they will not notice entrances, exits, or changes.

Contrast

How much a character or object being animated should stand out from the background.