Take a walk or do some short exercises. It is a better stimulation for your body than caffeine. You will gain natural energy and feel better. You should, however, not move too much if you don't want to look like you have just finished running a marathon.
Visit the restroom
Before the presentation, always go to the restroom and make sure you are not already wearing a turned on microphone.
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Article source Training Magazine - U.S. professional development magazine