Tips from the book...
When we cartoonists create a character to play a part in a story we're illustrating, the character must be believable. Posture, hand movement, stance, walk, and facial expressions are all means by which an audience comes to know and recognize the character. To identify with the character. These nuances and physical traits are impressions upon which we determine if we like a person or not. These characteristics must be included in the cartoonist's illustrated characters.
The cartoonist must be alert and aware of life around him. Pay attention to people. Study their expressions and reactions. Watch how different people stand, sit, walk, or run.
Outer characteristics will often indicate what goes on inside. Distinguishing characteristics distinguish the character.
While I've been trying to add little ticks to various CN:H characters, I know I'm not often able to pull it off. Just little things like the fact that Max's ears tend to be partially lowered compared to many of the other mice characters whose ears tend to be more erect. Or someone having slightly hunched shoulders if they're having a bad day, or a slight smirk which reaches their eyes if they're feeling a little smug. I'm trying, but I still find these things difficult to pull off. Practice, practice, practice.
"Personality is an unbroken series of successful gestures."
-- F. Scott Fitzgerald