It doesn't get any simpler than this. Psychologist Richard Wiseman, the author of "59 Seconds: Change Your Life in Under a Minute," demonstrates a quick test that can help you to determine whether someone is good at lying or not:

So, which side of your forehead did you draw the tail of the letter Q? If the tail ends up on the left side of your forehead (to be read by someone facing you), you're more likely to lie a lot because you are aware of how other people perceive you.

But if you drew the tail on the right side of your forehead (so that only you can read it), then you are probably more of an introvert and bad at lying.