I show a lot. I pack everything into the lorry and do everything I possibly can the night before.
I also find out how is easiest to plait a horse. My last plaited horse was quite happy with them in overnight, my current one would rub them out so I plait in the morning. I have also found that he is easier to plait in the lorry at the show as opposed to at home.
I always arrive at the show with atleast an hour before my class to ensure I have enough time to do things calmly.
Finaly the best piece of advice I was ever given was "Rosettes are won at home you only go to hows to pick them up"
If your horse is well schooled and prepared properly then you have done all you can do. A show is not a place to be working on issues.