1. Ask "Do you want a spot?" Sometimes the answer is no because the driver has a good skill level and wants to find their own line. Sometimes the answer is no because they have their own spotter.
2. Stand where the driver can see you. Let other people take photos.
3. Don't be afraid to halt the driver and make him back up a few feet to get a better line.
4. Handheld CB can be your friend.
5. When a driver gets through an obstacle cleanly, make sure to tell them they did a good job. But don't lie. If they didn't follow direction or didn't understand your hand signals, make sure to let them know what those signals mean.
6. Take control like a boss. Be authoritative.
7. Be completely silent if someone else is spotting...
8. ...unless they are about to drive someone into a rollover situation. If this is the case, halt the driver and take over (if you know what you are doing).
9. Remember there are some obstacles that can be driven through without significant pucker, but if you STOP in the middle you can get extremely tippy or worse. This is a good time to walk up to the vehicle and explain this concept to the driver. "You need to drive through this obstacle."