Body language is crucial to an outstanding performance. As an actor, it's your job to master your space. Get to know and understand 'personal space bubbles'. These vary culture to culture and person to person, but in general there are four distinctions:
Intimate space is close enough to reach out and touch or kiss someone. We generally reserve this space for family, lovers, and very close friends. Crossing into someone's intimate space when you're not intimate with them is an aggressive move. On stage, this means that you should, in general, stand close to your character's partner or spouse. Subtle non verbal cues (i.e., touching your partner on their back or arm) is often part of this close space bubble. Use the taboo of crossing the intimate space bubble when you want to dominate, intimidate, and manipulate your fellow characters.
Personal space is the most common space bubble zone we use. You can easily reach out to shake hands with someone and the distance makes conversation easily heard. We use this space when talking to friends or colleagues. It's also a space bubble used at parties and other social gatherings. A first meeting would definitely fall into this category. Entering someone's personal space bubble is a request to talk with you.
Social space is often used with people whom you feel are not a threat but you don't really want to interact with them. Parties, networking events, and large events fall into this category. You can notice this space bubble when looking at a room filled with people. Generally, you'll see small groups emerge in the crowd. These are the social circles; people who know each other or who want to know each other. Moving into someone's social space is a request to be noticed, and is most often used when flirting.
Public space is used with total strangers, particularly when you're unsure of the outcome of the situation. This space bubble leaves enough room between you and other people to make use of your fight or flight mechanism. You have the opportunity to see the other person's entire body, their hand gestures and posture, giving you a chance to 'read' them before you interact with them. Fight scenes often begin in a public space bubble.
Knowing and making use of these space bubbles on stage will give your performance depth and a true sense of reality.