New York photographer Annie Leibovitz can get her subjects to do anything. She's immersed Whoopi Goldberg in a bathtub full of milk, she's covered Sting in mud, and she's even convinced a pregnant Demi Moore to pose in the nude. Leibovitz's secret is connecting with her subjects. Minutes after they've walked in the door, her subjects feel relaxed, trusting and comfortable. In 2009, Leibovitz pulled U.S. president Barack Obama away from the Oval Office for a surprisingly peaceful family portrait.
It's hard to get good portraits when your family is stressed out. That's why, as the photographer, it's your job to project an air of calm over the scene. Speak softly, put on some music, and offer drinks to the adults and ice cream to the kids. The best photographers are masterful at establishing a rapport with their subjects. Since your subjects are also your relatives, you've already got a leg up.
Above all, never say "cheese." For some reason, many amateur photographers are obsessed with making sure that everyone has a big toothy smile before they click the shutter. The result is photographs filled with people cracking half-hearted grins. Some people actually look better if they aren't smiling -- and if you force your humorless brother to look instantly ecstatic, it's just going to look unnatural. So, instead of saying "cheese," just keep a constant conversation going with your subjects while you repeatedly take pictures. After a few seconds, they'll overcome their camera shyness and adopt an expression they're most comfortable with.