Take Your Time - The biggest mistake you can make is to mash the gas when attempting steep obstacles. Instead of stabbing the throttle, back down and analyze the obstacle. Try a slightly different line or a little more speed. Spinning tires don't provide nearly as much traction as tires that are stuck to the ground.
Avoid a Stall - While it is nearly impossible to kill the engine in a vehicle equipped with an automatic transmission, rigs fitted with manuals are much easier to stall. When the engine shuts off, power brakes and power steering essentially become manual. This can greatly reduce your ability to stop and turn just when you need it the most. Attempt to keep the vehicle running at all times if possible. If the engine does stall, attempt to restart it with the transmission in gear and the clutch out. A hand throttle is another helpful modification to keep the engine running while your feet work the clutch and the brake pedals.
Know what's Ahead - If you cannot see the other side of the hill or obstacle you are about to attempt, it is wise to get out and check ahead to make certain that it is safe. Once you are belted in and behind the wheel it is too late to worry about what is on the other side or if there is traffic coming the other way down the trail. Another reason to check ahead is to survey the terrain. Once you start up the climb, it is likely that all you will see is hood and sky.
Use Your Gears - The key to making it up (or down) excessively steep terrain is to pick the right gear. Too high of a gear and you risk stalling; too low of a gear and you might not have the speed to keep your vehicle moving. You want to have enough momentum to make it to the end of the climb without having to shift in the middle of the obstacle. This is generally easier in vehicles with more gearing options, such as dual transfer cases, or with automatics, since the torque converter provides a safe margin for error. Winch for Safety - If you think that there is a chance you might roll backwards off a steep ascent, or forwards off of a descent, hook up the winch to be safe. It is better to have the winch attached and not need it than to have to fumble to find the controller and unspool the cable in a precarious situation. Just remember not to run the cable over as you make forward progress.
Wrangler or Wrangler Unlimited? - A Jeep Wrangler and a Wrangler Unlimited (4 door) on the same climb will produce drastically different results. The extra three feet of wheelbase on the Unlimited means that on many obstacles, the front tires are already up before the rear tires reach the ledge. Similarly, on descents there is less chance the rear of the vehicle will try to pass the front. The tradeoff is maneuverability. The two-door Wrangler will be superior in tight trails and angled objects that require a good breakover angle.