Think of body language like not playing with a pen, sitting upright, not slouching and speaking clearly.
Think of perceptive questions to express that you're curious and have thought about the opportunity.
Interact, maybe, with the interviewer's twitter profile.
Do not be worried to declare you don't know an answer.
Eat properly beforehand - and no smelly meals!
Advice for those looking for employment:
"Read a paper or relevant blog that concentrates on the area you're looking for a role in. This will make sure that you're relevant on updates in the market and will also be useful in an interview and tells the company that you are serious."