Principles of Animation

Squash and Stretch

This principle is what gives the impression of how solid or strong an object may be. The stiffer an object is the more solid it seems. The more pliable the object the softer it appears. Take for instance if you dropped a baseball vs. a tennis ball.

Timing and Motion

The speed of an object or action gives your audience a better idea of whats going on in a scene. Timing takes into account the weight, size, and density of an object. By making two objects of equal size move at different speeds can make one seem lighter or denser than the other. For instance imagine the x's below represent each time that type of ball hits the ground after dropping it.

 

Anticipation

Anticipation is the preparation of an action and a good way to indicate what is going to occur. Anticipation can also be used to draw the audiences attention. It can also be used to reveal something that is about to occur. In the example below you see the guy bending at the knees and can anticipate that he is going to jump.

Staging

Staging is setting a scene so it is clear what is about to happen. In an action scene the eyes of the viewers will be drawn to an object that isn't moving and the reverse is also true.


Follow Through and Overlapping Action

Follow through is the termination of the action you anticipated earlier in the animation but not necessarily the end of the movement. Overlapping action is what you see when a bigger object stops but something smaller that is attached to it keeps moving for a few frames.


Straight Ahead Action and Pose-to-Pose Action

Straight ahead action is usually used for scrambling actions and is created by drawing frame to frame. Pose-to-pose action is used when poses and timing are whats important.


Slow In and Out

Slow in and out is what occurs between poses in a scene.


Arcs

Arcs are the paths the animation should take from one keyframe to another that gives a natural look and feel.


Exaggeration

Exaggerating is useful in emphasizing a scene or character but be careful to not overdo it.


Secondary Actions

Secondary actions are used to enhance what is occurring in a scene. You have to be careful not to let it detract from the scene though.

Appeal

Appeal in animation equates to an actors charisma. It is the likability of the character.


Solid Drawing 

The ability of the artist to use 3D shapes, anatomy, weight, balance, and light and shadow in his renderings.

Personality

This refers to the likability of the personality of the character.


If you wish to know more here are some links.
https://www.evl.uic.edu/ralph/508S99/contents.html
https://en.wikipedia.org/wiki/12_basic_principles_of_animation
http://www.cgmeetup.net/home/timing-and-spacing-in-animation/
http://www.animationbrain.com/solid-drawing-2d-animation-principle.html
http://www.siggraph.org/education/materials/HyperGraph/animation/character_animation/principles/personality.htm