First we start with Squash and Stretch. This principle allows characters to have a sense of volume, mass, and flexibility. When a ball hits the ground, it compresses, and then streches back upwards as it bounces. The intensity of how much a figure stretches can impact the effect. More stretchy and exaggerated figures imposes a light hearted, funny effect. Whereas less exaggerated figures give a realistic effect. Squash and Stretch is also applicable to facial animation to emphasize emotion. However, the character must always remain at the same volume. Back to the ball example, when the ball bounces it stretches upward, at the same time the ball should be getting thinner. The same thing happens when the ball hits the ground, it grows wider, but at the same time becomes shorter.

Anticipation allows the audience to prepare for an action the character is about to perform. When a character is about to jump, they bend their knees. When they are ready to punch something or someone, they wind their arm up beforehand. This telegraphs to the viewer that this major action is going to occur. Such as Squash and Stretch anticipation changes the effect the more exaggerated it is.

Proper Staging draws the audiences attention to the importance of the scene. It also connects the scene to the continuity of the story line. This is achieved through the position of the camera, character, or the lighting. Each action or expression from a character must be clear and easily recognizable. Overlapping multiple actions in one shot can overwhelm and confuse the viewer(this can be effective if this is your intention). This even includes the background. The background should be simple and compliment the character and their actions.

Straight Ahead and Pose to Pose are two methods of creating animation. Pose to Pose involves an animator drawing or keyframing key positions of the character throughout a sequence. Afterwards the animator fills the gaps with more poses; in 2D animation this would be more drawing, in 3D it;s simply adding more keyframes. Straight ahead is a technique where an animator draws every frame from beginning to end. This method, however, can distort your characters volume or proportions. Animators usually use this method for unpredictable or spontaneous actions such as a fire or particles.

Follow through is when a characters body stops after an action and all other parts continue to move. This includes hair, arms, ears or tails on animals, and clothing. Nothing on a characters body will stop at once. Overlapping action is when a characters body changes direction and their other parts follow behind. Some parts will move faster than others. Arms and legs tend to follow after the torso, while clothing and hair are more independent.

Slow in and slow out is the acceleration as the character begins to move, and the decceleration as the character finishes their action. To achieve this in 2D animation, an animator would create less drawings toward the center of the action and more towards the ends. In 3D, an animator would add less keyframes toward the center, or adjust the curves to flatten more at the ends of each action.

Most natural actions are performed in a circular motion. The movement of a hand or head will not be straight forward, but curve in an arc. However, mechanical characters are usually animated without arcs to achieve that robotic effect.

Secondary Action gives a scene more life and realism. It's purpose is to re-enforce the main action and give more dimension to a character. When a person is talking, they may gesture with their hands or give a variety of facial expressions. When someone is walking, they may be swinging their arms or stuffing them in their pockets. It also shows a characters personality or mood, which enhances the scene. Secondary action should not draw the audiences attention from the main action, it should only emphasize it.

Timing is the speed of an action. An animator can add more drawings or keyframes to slow down an action, while less drawings or keyframes speeds up an action. Timing also another way to show mood, character, or even mass. A person lifting a heavy object will be slower when carrying it to emphasize the object's weight. Quick actions from a character show surprise or fear, while slow actions can show boredem or laziness.

Exaggeration gives a scene more appeal. Live action film can be accurate, but when applied to animation it looks still and lifeless. An animator should overstate their characters actions, while still keeping the action believable. Exaggeration can also help emphasize an emotion or tone where it could be unclear if made more realistic.

This principle encourages 2D animators to give the illusion of 3D when drawing. This helps reinforce the sense of mass and volume. An understanding of shadows, anatomy, and balance is needed to achieve this. This principle is not exactly applicable to Source Filmmaker, but it's still very important to understand.

And finally, we have appeal. Characters should have charisma, appeal doesn't entirely mean the character should be likeable to the audience. It should be clear if they are heroic or villainous, angry or happy. A characters emotion should be clear and easily readable. Images should be compelling and pleasing to view, unless you are trying to achieve a disorienting effect.

And now that you know the 12 Principles of Animation, you can apply these to improve your own animation. If you still have any questions, or want to see more examples, here is a playlist of Alan Becker's take on the principles. He shows great visuals to further explain the concept.

https://www.youtube.com/watch?v=haa7n3UGyDc&list=PL-bOh8btec4CXd2ya1NmSKpi92U_l6ZJd