It is said that before a transport the horse has to work ! Because he's going to stay a long time standing without moving, so he has to be relaxed and has to work before it.
They day after, you should, as it's possible, let him relaxing because it's stressful for a horse to change his environnement, but don't leave him alone ! Try to reassure him as possible and talk to him, he's going to hear a familiar voice :)
To me, the best way to prepare your horse is the day after the transport doing a trotting with the horse. It's going to help him to get a better morale, and to spend himself and he'll be more relaxed for the transport. The day after, you should just walk one hour to eliminate the toxin, and let him in the paddock