I'll pile on the notion of being a handler first. That will help you understand the environment without the extra burden of the armor.
The only other thing not covered in the other posts is to be ready to have your picture taken. A lot. At a larger event, you will probably need your handler's help to get through the crowd if there are time-sensitive portions of the day. Also, look at some pictures from previous events and see what poses work well. Figure out what to do with your hands and blaster in advance and you won't have to fumble around during picture time.
Have fun!