Provide a cell phone number of someone at the event who will have it on for emergencies 

Have a special place for Santa to park - very close to entrance of event

Have someone outside to meet Santa - to show him the way and to load toys into his sack if needed.

Plan it so Santa can make a "Grand Entrance"

Have everyone participating in a common task (ie.Singing)

Place Santa's Chair so it has a great holiday background for photos. Leave room behind for group photos and please do not put Santa near a real fireplace burning.

Place payment in a Christmas Card so you don't have to hand Santa a check or cash and risk a child witnessing the transaction.

Keep the children together and occupied to give Santa a few minutes for his departure.