Prepare your bike with the saddle low. Prepare yourself by keeping your weight back. If very steep then right behind the saddle makes sense.
Choose a line with the least ruts and plan your route down. Stick to it. Keeping your weight back dig your feet into the pedals to keep maximum traction onto your wheels to hold you on. Feather your brakes but avoid braking if on any slab or whilst going over slippery roots. Avoid too much front brake that could take you over the handlebars. Let gravity rule and let your bike roll down they way it was built to.