The nerves can get to anyone on the actual day of their GRE exam. But the one thing that you should not forget is to shortlist at least 4 universities that you wish to apply to. Do this research well before the exam and make your list before the exam day. And why should you make that list? BECAUSE your GRE exam fee also includes sending your exam score to 4 schools for FREE. Yes. Here is the official verbiage from the the GRE website:-
"Your test fee entitles you to request that scores be sent to as many as four graduate institutions or fellowship sponsors. For the computer-based GRE® General Test, you will be asked to designate your score recipients at the test center. For the paper-based GRE General Test, you will be asked to designate your score recipients during registration or on your admission ticket correction stub. You will be required to pay US$23 per recipient to have scores sent at a later date."
So remember to make a list of 4 schools before your exam, and then send your score to these schools right after your exam if you are happy with your score. Any additional schools that you wish to apply to will cost you $23 a pop. However, if you do not like what you scored and decide to take GRE again at a later date, do not send your scores.