Rehearsal is the key to a successful performance. It's also the most effective method for reducing anxiety and calming pre-performance anxiety. If you know what you're going to do because you're well rehearsed, you'll feel more prepared and, thus, less anxious. It's not just repetition, but training. If you have to stop a rehearsal, start back up at the exact same emotional, physical, and energetic state. Otherwise, you'll lose the through-line and arc of the speech.