It is important to convince the entire group for a picture. So step outside your comfort zone, take pains and organise the group in an orderly manner. One way of doing this would be to make a rough scribble and figure out where everyone will stand. This scribble is only the foundation of the main shot and you need to remember that candid images and poses will happen on their own. Do not stick to the scribble if it is not working out. Additionally, be polite, yet firm while directing people in their poses. Keeping the crowd engaged is vital so that they do not lose interest and disintegrate. Keep talking, crack jokes and be expressive to engross the audience. Become a stand-up comedian if the situation demands it!