Never curry your horse the day of the show. That will add more grooming time to get rid of all that undercoat dirt. Take a rag and a sponge with you. I always take a damp sponge right before my class and wipe down my horse then run over with the dry rag. Helps bring in that extra shine. I never use show sheen or sprays of that kind cause they have a lot of silicone and wax in them that damage the manes and tails and drys out coats. Baby powder works wonders to make white extra white. Sand paper the hooves then apply polish to the hooves. The sandpaper helps remove any extra grime that gets caked on the hoof and so leaves a clean slate for you to apply the polish and will get a much cleaner even application.
That is all that I have for now if I think of more I will list it.
For hooves I wire brush them, use an electric sander or sanding block, and use steel wool to get that last shine. Then I use clear hoof polish on horses with white feet and use black SHOE polish with clear over top on horses with black feet. The shoe polish with clear over top make them look a little shinier. To keep dirt off I spray pam all over (helps the dirt not pack as bad too).