Don't leave yourself out of group shots. Remember to use the self-timer setting on your camera so you can join the action. First set up the shot, put your camera on a steady surface (tripods are the best), check the focus, enable the self-timer, press the shutter, and run like the dickens to get in the shot -- you have about 10 seconds before the exposure is made.
If you can, position your camera within flash range (10 feet) and use fill flash, as in this sample shot. You'll find that it puts a little extra twinkle in the eyes.