We always used to have a routine down for shows.
1. Arrive hours early or the day before if possible.
2. Longe. Get the willies out. If they buck, make them push past it and work. If they are looking around, make them push past it and work. Once the horse is focused on you and asking you "what next?" then be done.
3. Ground control. Get those feet moving. Take them into the arena, introduce them to the scary things, make sure they work if they lose focus on you.
4. Preparative riding warm-up. Incorporating your ground control by riding. Hip-disengagements, pivots, circles, changes of directions, until your horse is soft in the face and focused.
5. Finishing. Prepping your horse by working it for the class.
Work work work work work. That's all I can say! Good luck!