The best way to prepare for a polygraph test is simple: rest well, understand how the process works and answer truthfully. No tricks are needed and, in fact, trying to "fool" the machine with countermeasures usually backfires, because an accredited examiner detects them and they can invalidate the test. Nerves are normal —almost everyone has them— and the technique is designed to account for them: it compares your reactions to the relevant questions with those to the comparison questions, so being tense does not make you "fail". The test measures breathing, cardiovascular activity and sweating while you answer a questionnaire you will have reviewed with the examiner beforehand; there are no surprise questions. With validated techniques its accuracy is around 85-90% according to the American Polygraph Association. Preparing well is not about controlling your body, but about arriving rested, informed and willing to cooperate.
How should I prepare the day before?
Useful preparation is common sense. Sleep enough the night before, eat normally and avoid an excess of stimulants such as coffee or energy drinks. If you take medication prescribed by your doctor, keep taking it and mention it to the examiner; do not stop it on your own. And drop the idea of searching for "techniques to pass the polygraph" online: those countermeasures require training, guarantee nothing and usually leave a trace on the charts, which works against you.
What happens during the test?
The test starts with a pre-test interview in which the examiner explains every question one by one, answers your doubts and acclimatises you to the equipment. Then the sensors are fitted and the test is run, repeating each series of questions several times. During that time you only have to do one thing: breathe normally and answer clearly. Do not try to regulate your breathing artificially to "control" the result; what is natural is what gives a clean reading. The test itself lasts between 60 and 120 minutes and the full appointment between 2 and 3 hours.
What if I am very nervous?
It is the most common thing, and it is not a problem. The polygraph does not penalise general nervousness because it compares reactions: if you are tense, you are tense about every question, so that background tension cancels out. An experienced examiner knows how to tell normal nervousness apart from an alteration that does compromise the reading, and if they detect that you are not in a condition to be tested, they stop or reschedule instead of forcing a conclusion. Trust the process and simply tell the truth.
Prepare with whoever administers the test
The best preparation is to talk to the professional who will examine you. At El Polígrafo the test is carried out by Fernando, a polygraph examiner and forensic psychologist, with a Stoelting CPS Pro system; his training in psychology helps you arrive calm and well informed. You can see the test step by step or check the terms and price before your appointment.