Leave it to the refrain of a campy, Oliva Newton John, 80's pop hit to clearly lay down an important principle of strong acting. Body language. It is something that I've been looking at and paying more attention to in my own work over the years and is something I find consistently lacking in student work. Mike Wu and I gave a talk in our Pixar 2 class at the Academy on this very topic not too long ago. How a character holds him/herself physically provides a tremendous amount of information to the audience and provides the real truth in a scene as to who your character is and how he/she is feeling. The body language may support dialogue being spoken or, in appropriate circumstances, completely contradict it. Of course, in situations where there is no dialogue the body is your only means to communicate to the audience how your character feels. Why do you think news shows bring in body language experts after presidential debates or press conferences? It's because when it comes to communication, the truth is always in the body.
Having said that, bear in mind the context and content of your scene. The rookie move I often see is to start adding a bunch of extra poses and peppering the animation with arbitrary gestures that don't support or, worse yet, take away from what you're trying to communicate. Start from the ground up. What's going on? A guy is asking a girl for a date. How does he feel? Nervous. What graphic elements could I put into my pose that will help communicate that? Concave curves. A sunken or deflated line of action. How is he holding himself physically? He can't look her in the eyes. He's holding his arms in tight around himself. How is he moving? He can't stay still. Just as your animation should build in a layered fashion, working from the root outward, so should your performance build. Start with content and context, and gradually layer elements which help support those ideas.
Mike Wu showed a clip in class from "Godfather II" that shows a brilliant example of skilled, well choreographed body language. It takes place shortly after young Vito has killed the old Don of the neighborhood. He is now speaking with a landlord on behalf of a friend "asking him for a favor". Watch it with the sound off like we did. It is obvious that Vito wants something from this man and the landlord is very clear about his dismissive attitude toward this thug who has the audacity to demand something from him. Now, in the very next scene, when the landlord learns from the neighborhood who Vito is and what he has done, the physical changes are sheer poetry in motion. The landlord has completely changed his physical demeanor. Vito, on the other hand, has what amounts to be a single pose that says more about how he feels than any line of dialogue ever could. Absolute gold!
Study similar examples and bear these things in mind as you work out the foundation of your performances. The eyes can't do it all. Factoring in these elements is what separates the great acting from mediocre or bad. Now, as Olivia would say, "Let's get physical."