Sip on some water. Don't gulp a belly-full or you may belch or need to run to the bathroom. Sipping a little water will help to hydrate your body and soothe your throat.
Stand or sit up straight and practice breathing slowly from your diaphragm area. This is the area just under the center of your ribs. Slow breathing will help to relax you. This breathing technique also will help you to focus on how you should breathe when you are singing.
Warm up your voice. Athletes stretch to avoid injury, and you should "stretch" your voice to avoid injury as well. Sing softly through your range. Begin with the notes that are most comfortable for you to sing and slowly work toward the notes that are toward the higher and lower ends of your register. Glide through notes gently using an open sound like "ahh" or "la." Buzz your lips as well to increase blood flow and agility.
Stretch your body. Stretching will not only relax you before a performance, but it will also improve your blood flow. Blood flow is important to get the muscles involved in singing warm and ready to perform. Improved blood flow also contributes to mental clarity, which is important for remembering lyrics.
Avoid certain activities. Do not drink or consume dairy products just before a performance, as they can thicken your mucus and give you a clogged feeling in your throat. Do not drink sodas or alcohol just before performing, as these beverages remove hydration from your body. Avoid loud talking, singing or yelling so that you don't injure your voice.