How can I overcome my social anxiety?

I will soon have a presentation at my school, but the problem is that I suffer greatly from a social anxiety. I fear that something in my performance will go wrong. I know consciously that it doesn't matter what happens, yet my subconscious seems to always disagree and pushes emotions that makes me feel like I would die as a result of the presentation. What should I do to overcome this fear? Is there any sort of mental preparation I could do before the presentation?