Bump skiing requires agility, balance, and rhythm, all of which you can develop with some aggressive downhill trail-running circuits this fall.
Find a steep section of trail at least 25 yards long, with lots of rocks, roots, and debris. Practice running slowly down the trail, keeping your eyes up and visualizing the fall line as you go. Keep your upper body upright and relaxed and your knees bent to absorb the impact. Your elbows should be close to your body. Try to keep weight shifts to a minimum as you plant your feet.
Pick up the pace on your next rep, training yourself to look ahead and not at the obstacles under your feet. As you pick up the pace, resist the temptation to lean back: Many trail runners bend at the waist or get in the back seat when the going gets rough and quick. Just as on snow, this can (and usually will) lead to disaster (see "right" and "wrong" below). Do 10 reps on the trail twice a week, seeking more fluidity with each session.
A former ski instructor, Brian Metzler is the founding editor of Trail Runner magazine. He has competed in dozens of trail-running races, including Colorado's Leadville Trail 100.