Animation - Principles 10 - 12: Exaggeration, Solid-Drawing and Appeal

Exaggeration - Exaggerating a motion or expression can help convey an emotion by giving it more impact. By making a more extreme motion, the emotion is far more powerful and convincing as a result.

Solid Drawing - It's important to keep a character from looking flat and 2 dimensional by using perspective and 3D shapes to block out a character's sketch. It's important to avoid symmetrical lines, drawing curved lines instead to create a more natural, dynamic motion.
Drawing a character in a 3D environment can help with scale and staging.
Twinning in animation is where the arms, legs or other appendages are all doing the same thing, resulting in a stiff and unnatural animation.

Appeal - This principle assures that the animation is aesthetically pleasing to look at, applying character. through physical changes such as conventions that fit a genre or expression.
It's important to be realistic with how much you can draw per frame, adding too many details to a character's design that could go amiss could mean the animation takes too long and isn't completed by a deadline.
This can also be defined by a character's color scheme and it's important to not have an animation's personality conflict with the colors used to paint them.