Camera acting - or screen acting - is a lot different from performing in plays. Rather than acting in front of an audience, the camera is your audience.
Here are some tips for mastering camera acting:
Imagine your eyes are like magnets: they have the ability to pull the audience in. Everything you’re thinking and feeling can be reflected through the eyes.
Treat silences as lines. Film and television editing require reaction shots and a lengthy post-production process, so treat pauses and silences in the script as lines themselves.
Know your audience. You can’t directly see your audience, but you still need to hold them in your mind, and remember you’re acting for them, not the crew.
Learn the technical language of the film set. Get to grips with the different roles, shot sizes, and the intended camera movement. This will prevent you from having to constantly ask the DOP or director what something means.