Prepare for the event by thoroughly learning each song you will be performing. Do not assume you can "wing it" without rehearsing. Even the best singers have to practice their material before a show. The more familiar you are with the material, the less you will have to worry about forgetting how the song goes. Even if you already know the music by heart, practice it anyway because it helps reinforce familiarity.
Eliminate material that isn't working. If you have trouble singing certain notes you can experiment with higher or lower keys depending on your natural vocal range but if it isn't working in practice, chances are it won't work on stage. It's a good idea to work with as many songs as possible so that you can pick and choose the material that's easiest for you to sing without straining your voice. If you insist on certain songs that you are having difficulty with, practice singing scales to expand your vocal range.
Exercise before the show so that your energy level is up. Jumping jacks, sit-ups and jogging can create a feeling of well-being as long as you don't wear yourself out. Stretching your arms and legs can also improve your physical and mental state. Dancing while singing is another way to feel good about yourself even if the actual performance will just be standing with a microphone. Any physical fitness activities that you already enjoy can elevate your mood and help you forget about fear.
Singing requires proper breath control which begins with a firm diaphragm and relaxed upper body. If your throat feels tight or singing feels painful it probably means you are not breathing properly. Other problematic signs are weak delivery, shortness of breath, lack of vocal power and inability to sing correct notes. Do not force the voice to go beyond your range. Avoid raising your shoulders when taking a breath. Let your ribs expand with your throat open and relaxed. Limiting physical tension and singing from the diaphragm with free flowing air is the safest and most powerful way to sing.
Confidence is the key to self-control which will help reduce anxiety. Instead of worrying what the audience will think, commit to the idea that you will give them something memorable and enjoyable to think about. Take pride in your talent regardless of talent level. When you get on stage scan the crowd and try to make eye contact with as many people as possible. Think of people as fans or friends instead of opposition and think of yourself as a leader instead of a follower.