My greatest challenge as an illustrator is character development: Making your characters the same throughout the story, from many different angles, making many different gestures, and expressing many different emotions.
For me, the best way to develop a character is to draw them over and over (and over)—all the time. Do I have a pencil in my hand? I should be drawing my character. Create rules that this character’s face and body must follow. Little Mouse must have his eyes half way up his face, the main orb of his head must be the same width as his shoulders, the fur on his cheeks must resemble a football… whatever the rules are, draw them over and over (and over) until that’s all you CAN draw when you draw your character.