The life of the scene is all in what the character is experiencing. What thoughts go on in his head for each moment? How will he react to what is happening to him?
A lot of this is spent trying to make the character think before he moves. Make it clear that he is reacting to what is happening, not anticipating or driving the action. If a character is going to do some action, put the thought in his head, “Oh, I want to go do this.” Then make him go do that. If a character would simply get up and do something without thought, the scene feels a bit lifeless and less real.
Another way of getting into the character and how he would react is to think, ‘emotionally, what does he think of the situation that is going on?’ Is he gung ho about the event? Is he ambivalent about doing it? Does he do it begrudgingly but needs to put on a happy face? These are all questions I will ask of my character before starting a shot. This allows the life to breathe into him naturally.
So where can you put in this idea of thinking? The easiest place is in the eyes. The eyes are the window to the soul but they are also the doorway to your characters thoughts. There are all kind of books that will teach you about body language and more to the point, eyeball language (new term, just coined it). When a person lies he looks down. When he honestly doesn’t know the answer but is afraid to say he doesn’t know, he looks up (almost as if to find some divine inspiration). Looking around a room can show fear or anxiousness. Excited eyes are normally pretty transfixed on what has their attention. It’s almost as if they don’t want to miss anything.
Lemme give you a quick example of how powerful the eyes can be when dealing with emotion. I did a shot one time where the character felt sad for another character and really didn’t want to face him to show her sadness. I made the eyes be the last thing that “looked” at the character. The body got there first, then the head and then finally the eyeballs. It really sent the message of emotion from this character.
Think. Feel emotions. React. Eyeball language. (Trademark on the term still pending)