Actors sometimes get caught up in their dialogue: memorizing the lines, delivering them one way or another, etc. Never forget that the majority of actual human communication comes from body language, not words! Here's three tips to help you use your body language on stage to communicate the story:
Using a 'Launch Stance'
One of the most difficult things an actor is asked to do on stage is simply to stand there, saying nothing. Suddenly, you don't know how to stand or what to do with your hands. Using a launch stance is helpful in this situation. A launch stance is a relaxed and confident pose that claims your space on the stage. Keep your arms loose, your hands unclenched, and relax your shoulders. By doing this, your body immediately says to the audience: Yes, I am someone in this play; notice me.
Lean for Power
Leaning into someone's personal space bubble is an effective nonverbal move in several situations. People lean towards each other to show interest and compassion. But this can also be used to intimidate others, and in the right setting a simple lean towards a fellow actor can convey a bullying or overpowering relationship. Used effectively, it's a great comedic tool, too.
Gaze with Purpose
It's a natural reaction to look at someone who's speaking to us. Remember this while on stage! Not looking at a fellow actor when they're speaking can show disagreement, anger, disgust, or self doubt. Use your eye contact skills to give your character real depth.
By using these three simple tools, you'll be able to convey the story without words. Your audience will understand your character and your motivations, and your cast will really bring the story to life!