PRACTICE WITH A LIVE AUDIENCE
Simulate the nerve-racking environment by organizing a few live audience rehearsals. Perform your song, your set, or your entire show to a random audience such as your neighbors; or your parents' friends; or your close friends and their families; or even your co-workers.
Try to practice in front of a small audience first!
Chose your audience by asking yourself this question: Who will make me the most nervous? By creating this trying situation in advance, you will be learning how your body reacts to pressure. By the time you hit the stage, you will be much more self-aware. This is a great tool.
If you've repeated this simulation exercise a few times it will become second nature to recognize if you're suffering from a touch of nerves. This knowledge will calm you down and allow you to take back control of your body and voice.
You'll say to yourself, "I got this. I know my voice feels shaky right now, but when it felt like this before, I still hit the note. So, I'll be able to hit it now!"