When you design the most important part of your design is the Silhouette.

The silhouette should be:
1. Simple Iconic and memorable: Be appealing.
2. Communicate: Define the emotional tone of your character (even if the interior details and color are blacked out).


To complex and forgettable.

To simple and forgettable.

Just right ;)

(I believe Bill Perkins is responsible for this famous sheet. )

2. Communicate clearly:

There three basic emotional tones any piece of illustration or design will emote. Feelings of: 

Stability, Rest, or Movement.

Squares tend to emit a feeling of STABILITY.

Circles tend to emit a feeling of REST.

Triangles tend to emit a feeling of MOVEMENT.