Not all subjects are co-operative for photos during the holidays. When you don't have time to arrange people, lighting, or the setting as carefully as you' like, try these tricks:
For a family grouping, a plain wall or curtain can provide a nice backdrop. If you use a curtained window as the background during daylight hours, however, you may need to adjust your exposure to account for backlighting.
At night, you will need to use a flash even if you switch on room lighting. If your camera offers slow-sync flash or slow-sync red-eye flash, switching to that mode will help brighten the background. That's assuming the background is worth showing - if it's not, leave the flash in regular mode or red-eye mode, and your background will appear dark.

Speaking of red-eye flash mode, warn your subjects that they will see two bursts of light, and that the second one indicates that the flash has fired.
The first light appears to constrict the subject's pupils slightly, which helps reduce red-eye. If you don't give people this warning, they will think that the preflash is the real flash and stop smiling or move before the picture is actually recorded.

Don't always insist that people face the camera and say 'cheese' Instead, look for opportunities to catch a subject enjoying an everyday activity, which almost always offers a truer reflection of a subject's personality and is infinitely more interesting. Also, capturing interaction between people tells more about their relationship than the typical shoulder-to-shoulder arrangement that most people use for their family photos.

If you're trying to photograph very young children, fire the flash a few times before you really get serious so that they can get used to your presence. After a while, they'll forget that you're there, and you can capture them doing what they do best: being kids.