You know lots of different people with lots of different personalities. Each person reflects who they are by what they wear. Dress style can express age, gender and attitude. Get out that eraser. Take your tracing paper, lay it over your finished first draft and trace it with your black pens.
Color can also express attitude.
The same goes for people who dress in wild, colorful styles. Choose your colors and add them to your drawing. You can let out your animal instincts by adding human elements to a creature feature. Try a bird's head on a person's body or give your character a carrot nose. The only limit is your imagination.