If things are getting a bit stale when shooting a débutante (new) model, what I often do is frame the image move my eye from the camera and say to the model that ” I want you to take a deep breath and break for a second…” It is often at that moment I take the shot and more often than not it’s a keeper.
Another couple of techniques I employ is the close your eyes technique. I ask the model to close her eyes. I then either wait for her to freak out and open them, as they don’t know what is going on or I ask them to “OPEN!” at that moment the expression is usually out of the ordinary and their facial expression’s are really pretty amazing. As a result of this you get some really pretty dilated pupils. Also try the “concentrate on squeezing your forefinger and thumb together and only think of that pressure or apply pressure to the right or left ball of your foot… Or concentrate on a specific point on the wall and then scan the wall to the left or right. Watch what happens. The models expression has less to do with her concentration on her pose than “why is he having me do this or this is strange etc…” and what you get is often really interesting.
I will sometimes ask them to drop something and pick it up or throw something up in to the air. It can be an imaginary object or the real thing. I will also ask them to go through the bag they are holding and look for the object that I have placed in it. In the the look for my comb in my bag sequence, I will tell them not to look in the bag, just feel for it while looking in my general direction. Some of the stuff you get can be really interesting.
Using a fan often gets some interesting results, that is if the hair stylist is OK with that. Another little trick I sometimes employ is the placement of a mirror just to the right or left of me and facing the model so that she can see herself. The model is more apt to experiment when she can get some positive visual feedback. I have gotten some pretty good images using this technique as well.
Good Luck and be Patient.