A couple of things for spotting. The most important thing is trust between the driver and the spotter. Since the driver can't see, they must trust the spotter 100%, second guessing the spotter usually ends up poorly for the truck. The second most important thing to spotting, is that once the spotter gets outside of the rig, they are in control. The driver basically becomes the monkey behind the wheel, steering and applying gas as instructed, and only looking at the spotter. A third important thing to remember is there is to be only one spotter, and the driver should only listen to them, unless the spotter defers to someone else on the trail.
One other thing, try and not to get into the habbit(a bad habit IMO) of shouting which direction the driver should go, hand signals are far more effective, and is really the only form of communication needed while spotting(maybe I am just old).
