The person fingering his collar might be acting out nervousness or insecurity. To help you incorporate gestures into your characterizations, imagine you are the person in the story. Act out his role in a scene and see what gestures come to mind. Observe the gestures of people you know or of strangers with whom you come in contact. An effective way to observe gestures is to watch television with the sound off.
Eyes are probably the most commonly used feature to indicate character.
Suppose you wanted to show that Jim was cold and calculating. The mouth is another commonly used facial feature for indicating character. Laura's smile flashed on and off like an electric light. Now, let's move on to the larger actions a character takes in reponse to something happening in his external or internal world. His responses will depend upon his motivations, his basic needs, and his traits.