So I've assembled some advice for both here. Incidentally, I used many of the suggestions below to help myself through graduate school and beyond. Tips for students and speakers Take care of your body. Regular exercise reduces your heart rate. Caffeine and junk food increases it.
Excessive smoking restricts blood flow.
Try to eat something healthy before a class or a presentation so that your blood-sugar level is normal. Let your instructor know. Come to class prepared. Make sure you have completed the readings and assignments for that day's session. Have potential questions and comments written out ahead of time.