COMMUNICATION!!!
You gotta be able to understand what your other team member needs. The spotter has got to be able to know the limits of the rig, and the driver. The spotter has to know where all the cones are, and has to know how to communicate that to the driver. The driver has to realize what the spotter can't see (yup, believe it or not). A lot of times I will have a cone on my back passenger side, and my spotter will be watching the front tires and not see it. I can usually remember it's there, and will ask him how close we are. If he says we're okay, we're okay. It's also VERY important to come up with a game plan on every obstacle, and both team members must know the plan. It may seem like there's only one way to go through a course, and stay between the cones, but you really have to plan a course, and know which rocks you want to stay high, or low on, wich cones you want to hug, where you need rocks stacked, and other stuff like that. There's soooooo much more...