12 Basic Principles of Animation

1. Squash & Stretch

The purpose of squash and stretch is to give weight.
2. Anticipation

The purpose of anticipation is to prepare the audience for an action.
3. Staging
The purpose of staging is to direct the audience's attention to the greatest importance of the scene.

4. Straight Ahead Action & Pose to Pose

In straight ahead action, one draws out each frame. In pose to pose, one draws a few key frames and fills in the intervals later.
5. Follow Through & Overlapping Action

"Follow through" means that loosely tied parts of a body should continue moving after the character has stopped and the parts should keep moving.  "Overlapping action" is the tendency for parts of the body to move at different rates. These principles follow the rules of physics.
6. Slow In & Slow Out

Slow in and slow out exaggerates certain poses. The movement of the human body, and most other objects, needs time to accelerate and slow down

7. Arc

Most objects follows an arched trajectory.
8. Secondary Action

Secondary action supports the main action. It helps emphasize certain motions.
9. Timing

Correct timing makes objects appear to obey the laws of physics. Timing is affected by factors such as weight.
10. Exaggeration

Exaggeration helps emphasize the animator's intentions.
11. Solid Drawing

Solid drawing gives objects volume and weight.
12. Appeal

Appeal gives character and charisma to characters.