#1 Shoot the moments, not poses
It's tempting to run around and have people "Smile" or "Look over here!" A better option is to be a little more discreet and try to shoot the moments instead of poses. Talking, laughing, opening presents, sharing a drink - these are the moments you want to capture. The documentary style of photography allows you to shoot people just being themselves. Wouldn't you rather shoot uncle Al doing the Macarena instead of sitting in front of the tree?
#2 Get eye to eye with the kids
Some of the best photos often end up being the ones of kids. It’s fun to see them grow and change over time. Years later you'll have a great memories to look back on.
Most of the time adults will stand and shoot down on the kids. That make people look small and insignificant, we want the opposite. So squat down and take the image from their perspective, the results will be well worth it.
#3 Adjust the ISO instead of using the flash
Holiday parties can be dark and if your camera is on Auto it'll pop up your flash. The on camera flash casts weird shadows and is unflattering.
To fix this, put your camera on one of the program mode like Aperture priority or Shutter priority. Then raise your ISO. The higher you set your ISO, the less light your camera needs to take a photo. Your images will look more natural and you won't be blinding people with the flash.
Be sure to practice beforehand so you are comfortable not only setting the ISO, but knowing the limits of what your camera can do.
#4 Christmas light bokeh
This is a cool trick. With all the Christmas lights up this time of year getting good looking bokeh (out-of-focus parts of an image) will be easy. This tutorial from kevinandamanda.com puts a fun spin on things and allows you to add shapes to your bokeh.