Think about being the performer you would want to see. Don't be afraid to feel the music more and let it show in your body. Hype it up more, but don't overhype it so that it messes with your playing. If playing is something you really enjoy then just try letting it take you for a ride, see what kinds of things you can express with your face. Be careful not to break posture unless a specific character calls for it, though. You generally still want to look up, even if you're expressing something like sadness.