Composition

1. Can you see everyone's head?
2. Get in close so that background clutter is at a minimum.
3. Pose the group.
• Tall people behind and short people in front.
• Tall people in the middle. Short people on the sides.
• Avoid making the group too deep.
• Avoid lining up the heads in lines that are too straight. Curves, and triangles are more exciting.
4. How are their hands positioned?
• The side of a hand makes it look slender.
• The back of a hand makes it look strong.
5. Keep hands occupied somehow. Hands hanging limply look dumb.

Location

1. Does the location say something about the group?
• If you can, put them somewhere where they're comfortable.
2. Are there distractions in the background?
3. Don't take a shot right in front of a window. It will like mess with the light readings on your camera.

Other tips

1. Take multiple shots.
• People often relax after the first shot and you get a more natural response.
• Try putting your camera on burst mode.
2. Have everyone look up a bit. This will eliminate a lot of multiple chins.
3. Communicate. You're the photographer. Let people know what you expect.
4. Smile. The photographer staying positive helps the group stay positive.

Resources 

1. Digital Photography School
2. PictureCorrect.com