Reading Body Language and Facial Expressions!
Some children struggle with picking up on social cues from non-verbal language. Non-verbal language includes facial expressions, body language, gestures, tone of voice, and posture.
It is a great idea to talk about this with your child to better equip them in social situations. You can give them examples of different expressions (smiling, scared, mad, tired) and have them guess what emotion or feeling it is. You can also show them body language cues (turning your body towards or away from them, making good eye contact) and explain to them what it means (example: If someone is talking to you, your body should be facing toward them and you should look them in the eye). You may also want to explain the differences in tone when someone is happy or angry.
There is a cute (and free!) feelings game and story online that I like. It is an easy to play game (they also have a short movie) that the child gets to choose emotions based on a Robot's face. Check it out!