Screen acting often rewards specific behaviour more than the display of emotion. Small changes in attention, timing, and response can show that something is happening inside a character.
The core idea
Instead of deciding to look sad or angry, ask what you are trying to do in the situation: keep someone close, avoid a question, gain trust, or conceal a mistake.
How to apply it
Allow the other person to affect you. Listen, receive information, and adjust your next choice. The camera does not require every moment to be small; behaviour should fit the scene, genre, shot, and direction.
Try this next
Repeat a short exchange with one objective. Remove gestures that exist only to show the audience what you feel. Keep actions that serve the scene and observe whether the performance becomes clearer.