Looking further into Animation principles.

An in depth look at animation principles:


SQUASH AND STRETCH:
The concept is this... when a rubber ball hits the floor, it squashes out - it flattens a little. Then when it bounces back, it will stretch, or elongate slightly. This can be used to make things look very realistic or comical.

ANTICIPATION:
Instead of making things just happen, for example animating someone just immediately throwing an object and catching the viewer of guard it is important to draw the viewers attention to the action beforehand.


FOLLOW-THROUGH AND OVERLAPPING ACTION:
Follow-through is what occurs after and action has taken place. It is the direct physical result of an action.
An overlapping action involves movements that flow for instance, a man winding up for that pitch might start by only moving his arm, then his shoulders get into it, and then his torso, and pretty soon his entire body is winding up.

ARCS:
Arcs refers to the gravity of an object or the way it's formed. For example if a ball is thrown it wil not move through the air in a straight line and then fall flat down. What it will do however, is move through the air at an angle then when it falls down it will dip rather than fall straight to the floor and thus when the ball travels it is similar to an arc.

EASE-IN AND EASE-OUT:
Or in other words Acceleration/Deceleration. If something starts up such as a car, it will not instantly move but rather gradually get faster and of course gradually get slower.

TIMING:
You can break it down into essentially 2 categories... physical timing and theatrical timing. Physical timing refers to the actual motions required to perform an action, while theatrical timing refers to the pauses and the emphases added to make it dramatic.

SECONDARY ACTION:
Secondary Actions are little movements that aren't essential but that help to add meaning to an action. Example: a boy is lifting a sandwich up to his mouth to eat it. If he licks his lips along the way, it adds a shade of meaning to the action. Hence this is a secondary action.

EXAGGERATION:
This depends largely on what kind of animation you're doing. If it's realistic you might want to keep exaggeration to a minimum, but obviously for something more crazy or comical you can really go nuts. 

STAGING:
Most of the other principles have been written about mainly in animation books, but Staging is really not animation-specific. It's a director's tool, used in all kinds of filmmaking and stagecraft.

STRAIGHT AHEAD ACTION AND POSE-TO-POSE:
This one is really biased toward cell animation or CGI, since stopmotion by its very nature is always straight ahead animation. What this means is that you must start at the beginning of a shot and progress through it straight ahead, one frame to the next, with no going back and no jumping ahead - no second pass (unless it's in post production to add effects).

SOLID DRAWING The basic principles of drawing form, weight, volume solidity and the illusion of three dimension apply to animation as it does to academic drawing. The way you draw cartoons, you draw in the classical sense, using pencil sketches and drawings for reproduction of life. You transform these into color and movement giving the characters the illusion of three-and four-dimensional life. Three dimensional is movement in space. The fourth dimension is movement in time.

APPEAL:
You should try to make your work appealing. If people start looking at their watches a few seconds into one of your animations, maybe you need to work on your appeal.