12 Principles of animation

1. Squash and stretch
Squash and stretch give weight and volume to a character as it moves. It is used in all animation forms, from a simple ball bouncing to the body weight of a person walking. Also, it is used in animating dialogue and facial expressions.
2. Anticipation
Anticipation shows what the character is about to perform, for example, starting to run, jump or change expression and so on. Also, it developes a character's personality.
3. Staging
Staging is meant to clearly show the character's movements, expressions and story in the scene. Using one action clearly stated will give a good idea of what's going on in the story line. Background and animation should work together as a pictorial unit in a scene.
4. Straight ahead and pose to pose animation
Pose to Pose lets to plan movements and expressions with key drawings done at intervals throughout the scene.This lets the size, volumes, and proportions are in better control as you animate.
5. Follow through and overlapping action
Overlapping action is when the character changes direction while his clothes or hair continues following him. The character goes in a new direction, few frames later his clothes moves in the same stage as the character started to move from.
6. Slow-out and slow-in
As the action starts, we have more drawings near the starting pose, one or two in the middle, and more drawings near the next pose. Fewer drawings make the action faster and more drawings make the action slower. Slow-ins and slow-outs soften the action, making it look more realistic.
7. Arcs
Arcs give animation a more natural action and better flow. All arm movement, head turns and even eye movements are performed on an arcs basis.
8. Secondary actio
Adding more details in animation movements and expressions.This let us to enrich the main action and adds more dimension to the character animation. All of these actions should work together in support of one another.
9. Timing
A variety of slow and fast timing within a scene adds texture and interest to the movement. Allowing to add and express more feeling in it, for example, more drawings between poses give slow and smooth the action but fewer drawings make the action faster. A variety of slow and fast timing within a scene adds texture and interest to the movement.
10. Exaggeration
Exaggeration is used to push movements further to add more appeal to an action. Exaggeration can be used to create extremely cartoony movements, or incorporated with a little more restrain to more realistic actions.
11. Solid drawing
Solid drawing gives stable characters' form or face, which passively changes or moves from one frame to another. Which gives a clear view of characters or the object's volume, weight, height and so on.
12. Appeal
All characters have to have appeal whether they are good or bad. Appeal includes an easy to read design, clear drawing, and personality development that will capture and involve the audience's interest.