It takes a certain awareness for a photographer to capture that large group photo.
For the group though, the clothing can make a huge difference. When it comes to large family photos. If you dress in simple, coordinated clothing, you can show your family's unity. If you let your clothing blend into the same color tone as the backround and surrounding your faces become more focused.
Matching T-shirts (stay away from logos and brands (unless your showing your support for your favorite sports team). Blue jeans and bare feet for a fun style but keep it simple.
A stairwell can add style and creativity to the look of a large group. Being around a campfire or if your group or family has a common hobby show that unity. Let your imagination out and the ideas will grow.
Grab those special moments or milestones of your group. Capturing emotions make for the best group photos.