The Head

Rapidly nodding your head can leave the impression that you are impatient and eager to add something to the conversation -- if only the interviewer would let you. Slower nodding, on the other hand, emphasizes interest, shows that you are validating the comments of your interviewer, and subtly encourages him to continue. Tilting the head slightly, when combined with eye contact and a natural smile, demonstrates friendliness and approachability. The tilt should be momentary and not exaggerated, almost like a bob of the head to one side. (Do not overuse this technique!)

The Mouth

One guiding principle of good body language is to turn upward rather than downward. Look at two boxers after a fight: the loser is slumped forward, brows knit and eyes downcast, while the winner's smiling face is thrust upward and outward. The victor's arms are raised high, his back is straight, his shoulders are square. In the first instance the signals we receive are those of anger, frustration, belligerence, and defeat; in the second, happiness, openness, warmth, and confidence.

Your smile is one of the most powerful positive body signals in your arsenal; it best exemplifies the up-is-best principle, as well. Offer an unforced, confident smile as frequently as opportunity and circumstances dictate. Avoid at all costs the technique that some applicants use: grinning idiotically for the length of the interview, no matter what. This will only communicate that you are either insincere or not quite on the right track.

It's worth that the mouth provides a seemingly limitless supply of opportunities to convey weakness. This may be done by touching the mouth frequently (and, typically, unconsciously); "faking" a cough when confused with a difficult question; and/or gnawing on one's lips absentmindedly. Employing any of these "insincerity signs" when you are asked about, say, why you lost your last job, will confirm or instill suspicions about your honesty and effectiveness.