I have a relative who works for the NSA.  He told me has to pass a polygraph every 5 years.  He says that you can't use any tricks to fool the poly.  They'll figure it out.  Just act like you would every day and be honest.  Tell them every dirty little secret you have stored up in your head so you can make it less unnerving.  For example, if they ask you about whether you ever robbed a bank, you might think of the dollar you stole from your mom's purse as a kid.  You'll feel bad about the dollar and it will show up on the polygraph.  So, you have to tell them about it to get it off your chest so they can ask you a question like "Besides that dollar, have you ever stolen..."  The main reason people don't pass is because they don't open up to small things like that.  He says that nobody's a saint in the NSA and they have all done something they aren't proud of.  They don't care about those small things.  They want to catch the real bad guys.  As long as you haven't done anything bad while you were drunk before to get you into trouble, blown up a plane, killed somebody, or robbed a bank, you will be just fine telling them what is bothering you.  The main point:  Don't do anything seriously bad that you will feel guilty about or don't even try to take the polygraph.