In general, we communicate in three ways. We communicate through the words we choose. We also communicate non-verbally, through our facial expressions, gestures and body posture. Walk into the interview room positively and assertively. Don't shuffle in, yet neither should you storm in.
Elegance is the key.
Shake the hand or hands of your interviewer or interviewers, looking them in the eye and using their name. No wet fish of vice grip handshakes please. When shown your seat, sit with a straight back, looking alert and interested. Folded arms, hands in front of the face, head propped up on you hand all give inappropriate messages. Try not to fiddle with pencils, ear lobes, chins or locks of hair.