Research the barn know as much as you can about them, what shows, trainers etc
Do not ask about when and how long your breaks will be, or friends can come with you.Turn your cell off before you go through the door. Have a list of references with phone numbers and addresses to give to the manager. Be polite, do not chew gum or bring in a drink, water coffee of any kind. Smile and be honest. I think I would wear barn appropriate clothing. Clean and pressed. Good Luck.