First I just want everyone to know, the stuff you learn on this page really works.  I am not a bad person, but this firedept has very high standards.  I studied it for a month before I took my polygraph and I beat it.  I lied about everything pretty much, but convinced the polygrapher that I was an honest person by my body language, not squirming in my seat, eye language ect.   
The test consisted of a long pre interview followed by the test.  I was never asked a false positive.  He asked me 3 questions that were true, like were the lights on.  Then he compared all my questions against the ones that showed I told the truth.  When I lied i didn't bit my lip or hold my breath, because the chart would be elevated on its own.  When I told the truth I bit my lip and held my breath for a 3 count to elevate the chart.
In closing, convince the polygrapher that you are an honest person during the interview, and he won't think you are lying during the test.  Good luck.