When you want to build a connection with someone, body language experts say you should mirror their posture . But when you want to avoid conflict, your best bet is to shift your feet so that your body angles away.
Inc.com discusses the strategy in an article about body language:
When tensions are high standing face to face can feel confrontational. When what you have to say may make another person feel challenged, shift your feet slightly to stand or sit at an angle. And if you're confronted don't back away. Just shift to that slight angle. You'll implicitly reduce any perceived confrontation and may make an uncomfortable conversation feel less adversarial.
The full article has some other non-verbal cues that can help you in various aspects of your life, such as lying down to boost your creativity. I also liked the tip about "talking with your hands"; check out the post for more.