Put 'er there: Shaking someone's hand makes that person 42 percent more likely to give-in to your requests, shows recent research from France.
That's compared to not shaking hands before asking for a favor or service. (In the door-to-door experiment, the shakers were soliciting $1 for charity.) Tactile contact -- which also includes patting on the shoulder -- makes the person you're touching regard you more positively, and so boosts the likelihood that he or she will comply with your request, says study author Nicolas Gueguen, Ph.D.

Here are four more subtle persuasion tricks to try.

Mirror, Mirror
Synchronizing your movements with the person you're trying to solicit "emotionally binds you together," and so makes him more likely to grant your wish, finds a study from the University of Southern California. If the guy you're hoping to persuade crosses his legs, stands, or gestures a certain way, do likewise to gain his trust and approval.

Ask Twice
Because it's awkward and guilt-inducing to turn someone down, people are more likely to answer "yes" to a favor (and it helps you live longer) if they declined a previous request from the same person. So if your buddy couldn't help you move, he'll probably bend over backwards to give you a lift to the airport, indicates Stanford University research.

Set Them Free
Invoking your target's freedom -- e.g., "You're free to say no" -- before making your request more than doubles the likelihood he or she will cave in, shows another French study. By underscoring his right to refuse, you switch off his reflexive distaste for something that may seem like an obligation or imposition, the study authors say.

Mimic Infomercials
If you're offering something in exchange for someone's help, sweetening your contribution to the bargain with an "and that's not all!" add-on will improve the odds that he agrees, according to research from the University of Tampa. For example: "If you help me paint my apartment, I'll help you finish your deck...and I'll throw in a case of beer!"