Here are some good tips from a Scrapbook Etc article...
Group Photo Guide
Go Unposed
Not only can you get good smiles and good shots out of unposed pictures, but shooting while the subjects are unaware might lead you to an even better portrait. Shoot before and after the "posed" shots to catch more natural expressions and interactions. Here, Melissa Inman was able to capture a telling moment shared by her parents.
Photo by Melissa Inman
Shoot from Above
Photo by Shaune Lightfoot
Try shooting from above the group. When they look up to see you, each person's face will be visible and the angle will be flattering. In this photo, the approach also placed catch lights in the subjects' eyes.
Arrange People in Levels
Photo by Anita Matejka
Create a more dynamic shot by arranging everyone so their eyes are at a different level, as shown here. Eyes draw you in to a photo and by having them on different planes you'll gaurantee a dynamic shot.
Bring People Together
Photo by Tracy Kyle
In this situation, asking the subjects to put their arms around each other helped close a gap between them. It can also guarantee smiles as subjects play off each other's energy.
Form a Visual Triangle
Photo by Rachel Ludwig
When arranging groups, avoid static-looking rows. Creating a triangle formation, as shown here, gives the shot a sense of unity.
Capture the Kids with Ease
Photo by Christina Cole
When photographing a group of kids, take photos during play rather than forcing posed shots. By simply asking them to turn to the camera you can grab great personality shots with lots of impact without sacrificing the kids' playtime.
Place Your Subjects with Purpose
Photo by Christina Cole
Assemble your group and personally place everyone where you want them to stand. If someone is wearing brighter clothing, you may want to place that person behind other people or toward the center so that he is not as distracting. Important family members, such as grandparents, should be situated in the center of the group.
Place People on Levels
Photo by Leslie Lightfoot
Placing your subjects on different levels increases the interest in any group photo. Use natural or architectural elements to do this outdoors. Let everyone do what's comfortable, whether it's standing or sitting or jumping on someone's shoulders to get the effect.