MythBusters did a segment on this and they where not able to demonstrate a way to beat the test that was reliable. In fact, I don't think any of their "test subjects" where able to do so. Can some people do it? I think so. But I seriously doubt *you* could beat it unless you are a pathological liar who just doesn't care anything about truth, ethics or morals.
The MythBusters "Beat the Lie Detector" segment was particularly bad, and the producers of the show should be ashamed of it. You'll find a detailed critique here. In peer reviewed research on countermeasures, about half of programmed guilty subjects were able to fool the polygraph after a maximum of 30 minutes of instruction, and experienced polygraph examiners were unable to detect the countermeasures. See the studies by Charles R. Honts and others cited in the bibliography of The Lie Behind the Lie Detector.
The case files [...] suggest that the only people being "caught" trying to beat the polygraph are those using crude, unsophisticated methods that anyone who actually understood polygraph procedure and effective countermeasures [...] would ever use.
Did you mean "never use"?
Yes! Thank you.
That's precisely the official thinking about polygraph policy. Ten years ago, a senior instructor at the federal polygraph school floated the idea of criminalizing the public dissemination of information about polygraph countermeasures. I never thought it would come to pass, but it seems a considerable effort is being made.
What is wanted is not the will to believe, but the will to find out, which is the exact opposite. -- Bertrand Russell, "Skeptical Essays", 1928