Truthful acting means just that. It means don’t ACT for the camera but instead have an experience!
Feel what the character is feeling from moment to moment and immerse yourself fully into the role.
The camera is a great bullshit detector and if you’re “acting” then the camera will immediately read the performance as phony and contrived. Instead, you must have an EXPERIENCE when acting for the camera. And by that I mean experience everything the character is feeling emotionally.
The key is to be relaxed, learn your lines and don’t trip over the other actors.