Treat your voice with respect!
So what do you do to warm up?
1: Go somewhere quiet and (if you are self conscious as most of us are) somewhere private.
2: Shake out your legs, your arms, your shoulders and finally your head. Don't hold back! Get rid of all the tension.
3: Take a few deep breaths making sure that you are breathing from the diaphragm (hold your hand on your tummy to ensure that this is happening)
4: Release your breath slowly whilst running through the vowels. Open your mouth as widely as possibly and really stretch out your face. Repeat this a few times.
5: Read the first few lines of your speech or poem. Over exagerate.
You are all set. Stride on to the platform and amaze your audience!