Sir, you can prepare a very sound presentation, rehearsed in front of a mirror but the moment you climb the stage, your head would be blank. I personally am working on overcoming all these.
I actually find doing that very helpful when I was still in secondary school because we did a lot of presentation amongst our fellow student and it's a trick that I use to learn how to overcome stage fright. It was very useful back in the days, which I am still sure it will still be very useful today.