Characteristics to observe:
What do they do with their hands when they speak?
Do they appear strong/confident?
Are they nervous/shy?
What characteristics tell you that they are confident or nervous? What does their facial expressions look like, or their energy levels feel like?
What is the tone/volume of their voice when they speak?
Are their shoulders straight? Or slouched?
Do they tap their toe when they sit or do they remain still?
Do they cross their arms over their chest?