This is the time when you need to practice more and take some deep breaths to regulate your mood properly.
The only time I've ever performed was when I danced with my coworkers in front of the whole company at the annual meeting, and I know I'm the kind of person who's introverted to the extreme, and I usually feel very self-conscious when I talk in front of people. But at that time, we had been practicing that dance for a few months and were really skilled at it. So I felt a little more confident inside. I feel like proficiency in performing can really determine how nervous you are before you go on stage. You can recall roughly what you're going to say or do before you go on stage.
If you're already very good at it, then you need to be more mentally conditioned. For example, talk to others to liven up the atmosphere. You can also do more deep breathing to regulate your heartbeat. You also need to be prepared for failure, and tell yourself that even if you fail, it's just a loss of face, it doesn't matter. In fact, if you wear glasses like me, you can take them off for the performance, which will also make you less nervous.