Make sure he is registered to you and you take his paperwork. Make sure his tattoo's are in his ears and they match exactly his paperwork, if you can't see them shine a poweful light through his ears and see. If no tattoos tattoo him.
Get the rules early and follow them, if you need a health certifciate to show, than get on, soon you will find out that fair boards ask for these but goats folks don't even get asked for them, but a long time breeder doing this is much different than a new one.
Get him out of his pen, or trailer, our show makes you trailer or tie them away from the does, and walk him around the ring area during lunch, this will get him used to walking on whatever the ring is, like my girls do not walk well on sand.
I always use a prong collar, nobody will even look twice at you with it, I am not going to have to worry how my buck or big doe is going to react to a new judge or to another goat in the ring...just because they are fine at home does not mean they will be fine in the ring, and nothing is worse for a new person than being embarassed by a buck acting up! They also can't be seen to their fullest if they are dancing around, especially when the judge comes to feel of them.
Clean is the most important thing, which includes clean feet and clean under the tail. Then what Tracy said

Vicki