In animation there are 12 principles that cannot be ignored, and in all animation these 12 principles are used and followed to create the best animation.
Squash and Stretch
The first and very basics of all principles, squash and stretch tells the audience that all object gets stretch when traversing through the air or ground and gets squash when hit by an object or intercepted. The process is so fast a naked eye is unable to see this phenomenon.
Anticipation
Staging
Staging here refers to the same principle as staging in theater, its the background which helps the animation feels more alive than just a drawing
Straight Ahead and Pose to Pose
Straight ahead animation are animation movement done frame by frame, the create a very smooth and clean movement but very large file and time consuming. Pose to Pose however is the opposite, pose to pose as it's name suggested are animation movement created by moving from one pose to another pose. Our eyes takes the first pose and then the second pose then our brain will fill in the empty poses in the middle automatically, this process is much less time consuming but the animation will be less smooth in terms of frame rates.
Follow Through and Overlapping Action
Follow through are actions or movement that follows the first or primary action but they do not have the same force or friction or purpose as the first one, they are just following along if the primary action stops, the follow through action might stop together or might not, they are not affected by the primary action. Overlapping Actions are actions that moves together with the primary action but at a different rate or time frame than the primary action, for example an arm does not move in the same pattern as the head.
Slow in - Slow out
Slow in Slow out animation defines the physics of the animation world because it is use to refer to the frictional force of animation. In real life a car will moves slowly accelerating it's speed before moving very fast, in animation the same principles is used. a pendulum will start to drop slowly and then moves very fast towards the center and up it goes starts to slow down as it moves away from the center.
Arc
Arc are lines that we do not see in animation but its there to make life to a character. All natural beings moves in a arc trajectory like the arms or limbs, even a thrown object with the exception of mechanical lifeforms where they moves in a straight line instead of an arc
Secondary Action
Secondary actions are action that happens because of the primary action, they do not affect the primary action but secondary action exist to support the primary action to add in life into it. For example, a moving person is walking with his feet at the same time the arms are also flinging together this adds in the natural feel into the character.
Timing
Timing for animation helps to tell a story when used at the right moment or to help make the animation more realistic by adjusting the timing of the frames
Exaggeration
Exaggeration is a useful tool in animation especially cartoons or animation that doesn't reflects reality. This principles helps to create a situation and boosting its effect by applying exaggeration.
Solid Drawing
Solid drawing gives a character weight and volume. Solid drawing is mostly used to give the character a 3D effect.
Appeal
Appeal is used on cartoon characters to create a charismatic feel, to make a character interesting and appealing