Tell a spectator to think of a number between 1 and 100, ignoring all the "teen" numbers and all numbers that have an even digit. Chances are the number chosen by the spectator will be 37.
Forcing a Card Choice
Flip through a deck of cards facing the spectator so that both of you can see the faces on the cards rapidly shuffled. Tell him (or her) to glimpse at one of the cards being shuffled and to remember it. In secret, slow down the flipping process imperceptibly at one card, and then continue through the shuffle. The hesitation should be brief and unconscious to the spectator, but not to you. The spectator should mentally select that card, without knowing why. After the cards are flipped through, pretend to "guess" what it is!
Think of a Vegetable
It's a matter of suggestion, limited choice, and mass-culture reaction. Instruct the audience to perform simple math operations, like "2x3", "4+2", and "3+3". Then tell them to THINK FAST of a vegetable.
Over 90% of the time, the response is "carrot". (Less frequently it's "celery".) Display a slip of paper with "carrot" pre-written on it...and then smile mysteriously!
Please note: Perform this trick only in the U.S.A. It's a culture-based tic.