This is a much shorter post than the lengthy screeds on the material and delivery aspects of training, mostly due to the fact that this is the aspect of training delivery you have the least amount of control over as a trainer. But, admittedly I do have less to say about this area as well.
Fundamentally, a good training venue is one that can keep the trainer mobile, and the students awake. And, given that keeping the instructor mobile is about keeping students awake, it fundamentally boils down to keeping the students awake. The rest largely takes care of itself.