For anyone in customer service (or works for many different situations, but CS is a big one) put a mirror behind you at the counter. This way angry customers who approach you will have to see themselves in the mirror behind you and the chances of them behaving irrationally lowers significantly. No one wants to see themselves act like a dickhead.
When you first meet people try to notice their eye colour while also smiling at them. It might be because you look for a second or two longer, but all I can tell you is that people really respond to it.
For interviews I recommend altering your psychological state beforehand. Tell yourself “I’ve known these people all my life. We’re old friends catching up. I can’t wait to see them.” Visualize the experience, shaking hands, making eye contact, having conversation. What things can you not to wait to tell them? Hold an open pose…stand with your legs apart, hands on your hips, and shoulders back while doing this and SMILE. This may sound cliche but you are in charge of your own psychological state and the power of suggestion is strong.