Try to have one person operating the equipment and another doing the interview. If your subject can participate in a conversation you'll get better results than if they must talk directly to the person behind the camera. Remember, you have the opportunity to create an entire environment that can communicate something about your subject. Some family events lend themselves naturally to storytelling. Keep your camera with you, but be sensitive about intruding where it may not be welcome.
Family reunions are usually excellent times.
Taping at a funeral also brings home the urgency of getting older people on tape sooner rather than later. Take care of your taped interviews when you are done. Generally, videotapes keep better in the plastic cases used at libraries and video stores than in the cardboard sleeves they are sold in. Also, remember that tapes need to be stored in the same temperatures that humans tolerate well. In other words, don't store them in the attic in summer or an unheated basement in winter.