The principles of Animation

Arcs

All actions, with a few exceptions (for example, mechanical devices), follow an arc.

Arcs give animation a more natural action and better flow.

This would be used when creating a walking cycle or any kind of movement in a character as body parts need to move smoothly and this is achieved via using arcs.

Follow through

When the main body moves all other parts follow behind. when the main body stops the rest has to catch up, causing the main body to be still while movements still occur.

This could be seen in a glass being slid down a bar counter top. The glass will be caught by a bar patron but the drink inside will be moving inside the glass still and may go over the glass rim.

Exaggeration

Remaining true to reality but giving it a more wild and extreme form to add character to the animation.

wile e coyote will run off a cliff and float there for a moment before falling, this gives character to the show and also adds humour. Furthermore, road runners legs are drawn as just a circle that is spinning under him. this makes you think his legs are moving fast and removes the need to draw them as well.

Appeal

A quality of charm that is the charisma of the action.

If you make a action unique to a character in some way it will appeal more to the viewer. For example a signature move in a action show.

Secondary Action

An additional action occurring to further reinforce the main action and add more dimension.

For example, a character taking their hat off may have their hair flow down out of it.