Expression and traits are what finalize your character design. Expression for example can be as simple drawing posture or mood face Expressions. Finally Traits are why the first to sections are important these can be connect to both the character and the world.

The human face has a long list of expression to chose from and be applied to characters. The key is not to limit yourself pick and go for what works. Your charater wont always get the chance to speak. So expression really brings the character to life.