There are a few important things to observe in a candidate during the interview.
Firstly the most important thing is body language.
The few following gestures are made by a candidate who has good body language:
1. Starting with a handshake
2. Straight posture
3. Using hands while speaking
4. Nodding head while listening
I've always sworn by the mantra "motion creates emotion." Being physically animated and enthusiastic during a conversation, no matter if its in person or on the phone, captures the attention of your audience and creates a contagious effect in the discussion.
As more then 80% of communication is going by body language it's important to be aware of it. Only a few percentage is "manageble" the rest is "build in equipment of our non-manageble part". So, do use it? As far as I'm being able to manage, I hope I manage it well. For the rest I'm more focused on the reaction I get back from my body language. It's not how I use it, It's all about it's impact on others. That's the part I can manage.
To reinforce my major points when I'm speaking, and to show interest in what other people are telling me.
One way I believe is called modeling - where you copy the other person, like a mirror image, to get in step with that person. I don't really know if it works. I think I sometimes do this unconsciously.
What an awesome question.
As Reed said, eye contact, smile, solid hand shake, etc.
Here are two links fro Forbes:
How you use your body language depends both on how your audience views it (what impression they form), and how you wish to be seen by your audience (what impression you want to leave). Ideally, you need congruity between the two. So what impression are you trying to leave? Likeability? Credibility? Competence?
To my advantage. Of course eye contact is a must but, leaning forward and moving closer to the speaker is always a great way to show your interest in the speaker.