The larger the crowd, the larger and slower the gestures. If you have a small crowd, or if you are videoconferencing, or on television, use smaller gestures. Work to eliminate distracting or nervous gestures, but do not kill yourself to add new ones. They will take care of themselves and most of the time they look affected. Let your words trigger your actions. If you are counting, hold out your fingers. If you say no, shake your head no. Hold your hands open and wide apart to show sincerity and honesty. Hold your hands behind your back during question-and-answer sessions (don't overdo it). Avoid excessive hands in pockets, clenched fists, pointing, hands on hips, and the infamous fig leaf position where your hands are crossed in front of your groin.
Advanced Public Speaking Institute