In order to correctly prepare your voice to performance, you should carefully make sure to relax your sound-producing muscles while producing the sound.
An effective way to do that is adding vocal vibrations exercises to the vocal warming up, thus relieving the vocal cords strains and tension. A common way of preparing your voice to perform is a humming exercise: hum a song, a training piece or a single sound, with many light vibrations. At high pitches, significantly decrease voice intensity. This way, you redirect the resonance to your head cavities.
Faithfully keeping your voice intact