A self hypnotic "Blitz"- exercise for public speaking. Of course, you cannot only use this exercise for public speaking, but for anything else as well, any situation you would like to feel comfortable and confident in. I myself used it, when I prepared for my oral exam as a mental health practitioner some time ago. I am not a fan of exams and this was a very important one for me and I didn't want to mess it up with my nervousness.
It did work!
I did it every day for about a week before the exam and when it was finally the the day of the exam I dreaded, I felt surprisingly calm. I didn't have a black out during the exam, I even enjoyed it and it was over as if it took only 5 minutes. So from personal experience, I recommend practising it.