When I've run haunts, I was in charge of actor training and it was something that I focused on year round (we did lots of activities, seminars, and acting games in the off season). When we had new actors show up during production, I would work with them before the show opened and talk to them about the room, their ideas for their character, and make sure that I put an experienced actor in with them. Throughout the night I would go into that area and "play" with the new actor and give them pointers, fix any bad habits, and make sure that they aren't getting frustrated.
I believe your actors are some of your best assets, so proper education and training is a must. They should also be treated well (a little appreciation goes a long way) and I've used "Best of" awards each night to promote them to strive to be the best.
I love training actors and it is one of my favorite things to teach, whether it be at a Con or at a haunt.