Practical experience is always the best training in my opinion. Our training is simple and effective:
Sit all the actors down in a room and go over the rules, guidelines, etc. of acting in the haunt.
Get them all into "some" makeup and costume and have a dress rehearsal.
Invite out 20 or so of your family/friends and get them into 4 groups of 5 (or something like that) and keep cycling them through the haunt for an hour or so (you and your other managers, etc. going through as well giving pointers as you go).
Works really well to get them experience before they go live to the public. Especially if they're new.