Practice makes perfect. Or so they say. When you have to perform in front of people, it can be extremely nerve-wracking. There are only so many things you can practice for any performance. When it comes to the real thing, there are so many unpredictabilities, but those are exactly the things you shouldn't worry about. What you should worry about is properly doing the things you can in advance; focusing on breath, focusing on posture both before and during, trying your best to memorise the lines. But also equally, not getting worked up when things don't go as planned. That's what unpredictabilities are, and by definition they can't be prepared for, so make sure you focus on what you can actually control.