12 Principles of Animation

Squash and Stretch
To give a sense of weight and flexibility to drawn object.
The volume of the object does not change during the squash and stretch.

Anticipation
To prepare audience for an action, and to make the action appear more realistic.

Staging
To direct the audience attention, and make it clear what is of greatest importance in a scene.
To keeping focus on what is relevant, and avoiding unnecessary detail.

Straight Ahead Action and Pose to Pose
Straight ahead action means drawing out a scene frame by frame from beginning to the end.
Pose to pose involve starting with drawing a few key frames, and then filling in the intervals later.

Follow Through and Overlapping Action
To render movement more realistically, and help to give the impression that character follow the laws of physic, including the principle of inertia.

Slow In and Slow Out
The movement of the human body, and other objects need time to accelerate and slow down.
More drawing near the beginning and end of an action, emphasizing the extreme poses, and fewer in the middle.

Arc
Natural action tends to follow an arched trajectory, and animation should adhere to this principle by following implied "arcs" for greater realism.

Secondary Action
Adding a secondary action to the main action gives a scene more life, and can help to support the main action.

Timing
Timing refers to the number of the drawings or frames for a given action, which translates to the speed of the action on film.

Exaggeration
An effect especially useful for animation, as perfect imitation of reality can look static and dull in cartoon. The level of exaggeration depends on whether one seeks realism or a particular style, like a caricature or the style of a specific artist.

Solid Drawing
Solid drawing means taking into accounts forms in three-dimensional space, or giving them volume and weight. The animator needs to be a skilled artist and has to understand the basic of three-dimensional shapes, anatomy, weight, balance, light, and shadow.

Appeal
Appeal in a cartoon character corresponds to what would be called charisma in an actor. The important thing is that the viewer feels the character is real and interesting.