Keep your speed up as you approach. Most riders make the mistake of slowing too much to scope out the hill, forcing them to use too much throttle too late. This results in wheelspin or wheelying.
Scan the trail and look out for big obstacles, such as logs or rocks, that may be best tackled standing up. Also, don't just follow another rider on the same line; you may get trapped if he makes a mistake.
Most of the time, in the absence of any big obstacles, the best position on the bike is sitting. In this position, you can have the best compromise between weighting the rear wheel with your butt and keeping the front of the bike down with the weight of your shoulders and head. Weight the outside footpeg and put pressure on the gas tank with your outside knee.
Once you have made the initial turn and are on the hill, keep the power on, but smoothly.
With a hill this steep, if I were to pull up on the handlebar with my arms to keep me from falling backward off the bike, the bike would tend to wheelie. While if I use my abs instead, the weight of my upper body will push down on the front of the bike instead of lifting it, letting me keep the power on and keeping my speed up the hill.
Use your body to keep the bike as vertical as possible. If the bike is vertical, the rear tire will have the best traction and won't want to skid sideways out from underneath you. Here I am starting to move my upper body to the left, in order to keep the bike straighter, so I can keep the power on.