Obviously speed plays a role in off-roading and adages vary, but a good rule of thumb is to go as slow as possible and only as fast as necessary. In rough stuff, maintaining momentum is far preferable to reaching a high speed. Keeping the power reasonable and steady also means the vehicle is less likely to break something than if tackling challenges at great velocity. Novice drivers frequently inch the front of their vehicle over an obstacle and forget about the back wheel placement, landing with a resounding thud and irritating rear-seat riders. Having a "spotter" outside the vehicle can provide welcome guidance, especially on treacherous, rocky terrain, as the driver can't see directly under the vehicle for clearance and proper tire placement.
On surfaces like sand and mud, some wheel speed is beneficial. With mud particularly, be sure to find out how deep the mud is and what's hiding beneath it, such as sharp rocks, before committing. Sand presents its own challenges, with a very soft surface that often requires dropping tire pressure, and it rewards smooth pedal and steering-wheel application-an analogy is operating the controls in slow-motion. On sand, you should rarely need the brakes, as most vehicles will quickly slow to a stop without building a braking ridge in front of the tires that you'd later have to overcome. On some sand descents, the vehicle may want to slip sideways. The best way to get the back end in line is to step on the gas so the front wheels pull it straight again. This takes some getting used to-except perhaps for those accustomed to driving older Porsche 911s.
In open country, speed can actually be helpful. Some dry wash rutting can be minimized at 40-plus mph, because the tires don't hit every bump and vibrate through the truck. If you're driving quickly on dirt, beware of upcoming changes in terrain, which often can be identified by a change in surface color or increased vegetation, which indicates a low point where water is more plentiful.
Because of their gearing and traction, 4WDs are capable of much steeper ascents and descents than cars, so much so that you may not be able to see what's over the over the hood of the vehicle at times and therefore should adjust speed and deploy spotters as necessary. Unlike your mountain bike, vehicles are most stable when going directly up or downhill (if it's really steep, keep an eye on oil pressure) and not sideways along it. Should you miscalculate and roll your vehicle onto its side, don't panic. Low-speed flops usually do little mechanical damage, and injuries are typically related to unsecured cargo bonking you on the head; the passenger now above you releasing his or her seatbelt before you're out of the drop zone; or a hand grabbing a roll bar getting crushed. If in a Jeep Wrangler or other open vehicle, make a habit of never holding on to the roll bar when things get hairy.