Move forward on the saddle. For the steepest climbs, you need to be on intimate terms with the extreme nose of your saddle. Slide all the way forward, grab those bar ends and concentrate on pedaling smooth circles up the smoothest line. Gut-busting climbs are where clipless pedals really shine. The ability to haul back on one pedal with your hamstring while mashing the other pedal with the opposing leg's quads radically increases your torque and the range of slopes you can climb.
Clipless pedals are worth their weight in gold.
On technical, free-fall drops, you butt has to be over the rear axle. Here, unrestrained momentum is your enemy. The key to keeping things under control is your front brake, which is incomparably more efficient than the rear brake. I like to get so far back that I actually place my chest in the seat itself. Sometimes the only way to clean a section is to come to a complete halt, balance for an instant and then move off on a new line.