Eye contact, make sure your personality seeps through(for your own comfort), and make sure they leave thinking you are the only eligible person for the job. Employers like to hire people that will gladly give themselves for another. Customer Service, Retail, etc. They want someone who wants to devote every last cell in your body to them, as if nothing else in life mattered. Try to talk to them instead of worrying about what they think. Don't over extend though. You are here for them, not the other way around. Um...i don't have many donts. But good luck!

Dress nicely and definitely practice!! I've really found this to make things easier for me.