When is your first show? Will it be in the early spring or late spring?
If you have an early spring show, I would suggest you start blanketing him (it will help to make him shed) and I would also curry him a lot (it will help get out any hair that's already coming out) You can also use a shedding blade too. Or if you feel comfortable and are good at it, I would clip him.
If you want to, you can put his tail up in a tail bag so it stays nice and clean. (Just make sure to take it down once a week to take the braid out, brush it, re-condition it, re-braid it and put it back up).
Depending what you want to do with his mane (this will depend on what type of show you're doing) you can either, band it, braid it, or let it go naturally. You might want to shorten it if it's long.
To make him stay cleaner, you could put a blanket on him when he gets turned out.