The following transmission information is specific to Jeep Wranglers or vehicles which have had the neutral safety switch disabled. The information does not apply universally to all makes and models of vehicles.
Automatic Transmission
Use low gear and low range. I suggest the two footed driving method—left foot on the brake and right foot on the throttle. Feather both lightly to control your speed. If the vehicle slows down you may have to apply a little brake. Speed and power are not the answer! GO SLOW—the slower the better.
Manual Transmission (Driving Without the Clutch)
Use low gear and low range. If your vehicle has locking hubs, be sure they are engaged. Start the vehicle in gear WITHOUT THE CLUTCH. KEEP BOTH FEET ON THE FLOOR. To start: Turn the key. Do not use the clutch and apply only slight throttle as needed. Drive slowly and crawl over the rocks and rough terrain. Idle over rough spots—slight throttle only as needed. KEEP YOUR FEET OFF OF THE CLUTCH. If you start to slip or spin, apply a little more throttle and TURN THE STEERING WHEEL ½ TURN BACK AND FORTH. This will often provide a new grip. The important thing is to keep the vehicle moving. Keep your foot off of the clutch. Crawl over obstacles; THE SLOWER THE BETTER. Do not spin your wheels. To stop, just turn the key off. NO CLUTCH OR BRAKE IS NECESSARY. If the engine stalls going over a rough spot, do not use the clutch or brake. Simply turn the key again and apply very slight throttle if needed.
Source: Mark A. Smith’s Guide to Safe, Common Sense, Off-Road Driving