By taking 10 or so deep breaths, it can help calm your nerves. That's a lot easier said than done. It's not like students can just walk away from the exams. Well, they can. But that might not be the brightest idea and would probably cause more stress in the end.
Students can get away temporarily, though.
Maybe a trip to the rec center, Maxwell's, the art museum or a park will clear your mind temporarily. It can be pretty hard to study when you have music playing, a TV in the background, your phone ringing every five minutes and people knocking at your door. Once that temptation is there it's pretty hard to keep your nose in the books. When getting ready to hit the books, it's a good idea to get rid of all the distractions. Turn off the TV and radio.