Position yourself away from the camera in a group shot. The closer you are to the camera, the bigger you will look in comparison to everyone else. If you want to look thinner and smaller, you should try to be further away from the camera. However, if the camera is centered and you're standing in a line of people in a row, like if you're posing for prom, then you should try to get as close to the center of the group as you can. People on the ends of rows look bigger.