When I was competing moguls still (like 4 years ago) I thought it was all bullshit, I hated pre-season training, but after 2 years of not doing it I realized that they were actually on to something.
Everyone who has taken this post sesiously has brought up good points. Work your legs, but work all the muscles evenly (quads, Hams and calfs), work your core, abs (upper lower and oblique) as well as lower back, work some cardio, still work the rest of your muscle groups too (Otherwise you'll be this funny lookin thing with huge legs and abs but with little chicken arms and no chest!) so work it all evenly. as well the explosive power is a good one, (jump squats are great) Make sure you stretch....alot. A good warm-up stretch to start and then a nice long stretch when you're done, this helps prevent getting hurt when you crash but also it makes grabbing and what not much easier.
To those of you who didn't take it seriously, you're young now but just wait, after a few years and a bunch of hard bails, your body isn't gonna recoup so fast and it's gonna suck, cause you're gonna eat shit one day in the park or off a cliff then the next day you'll wake up at 8AM, look out your window at 3 feet of fresh and be so sore that even if you do make it to the lift it's not gonna be an enjoyable ride down. If you start taking it seriously now you'll prevent that in the long run, you think Douglas has been doing this as long as he has by sitting on his ass all fall? I doubt it.
Just something to think about.