Try on your mask to ensure it fits properly. A mask that is too large or too small can make you uncomfortable and severely hinder your performance. Inform your prop master if the mask is the wrong size and ask for an adjustment.
Choreograph your movements before you don the mask. The mask can severely limit your vision, so it might be difficult to find co-stars and perform prop-related actions. Practicing your movements before show time teaches your body to act on memory instead of using visual cues.
Wear your mask regularly before your performance to acquaint yourself with the limitations it poses. Practice your stage movements with the mask on.
Practice your projection with the mask on. A mask can severely muffle your voice, making it difficult to hear anything you say.
Don your mask before the performance. Have an assistant on hand to tell you whether the mask looks straight. Remain calm and say your lines once you head out on stage.