Staying in Shape in the Off-Season
Cardio: This can be anything from running, biking and hiking to anyone of those crazy contraptions at the gym with the Tv's on them. Cardio should be done 3-4 times a week for at least 30 mins each time. If you are just getting started start with 15 mins 3 - 4 times a week and gradually increase 1 - 2 mins each week till you get to 30 mins.
Strength Training: This is going to keep your legs strong so that injuries are less likely to occur, especially in the knee area. Strength exercises should be done 2 - 3 non-consecutive days a week. 1 - 3 sets of 8 - 12 repetitions each, or to muscle fatigue. Again if your just getting back in to it, start with less reps and gradually build up. Great strength exercies are Squats, dead-lifts, lunges and side-step hops.
Another important focus should be core strength and flexibility. Core strength will improve your skiing ability and can be strengthened by ab and back workouts and core centered activities such as pilates and yoga. Flexibility will help all these other workouts, it will also help greatly reduce injuries.
The main thing to remember is you need to keep your head into it - the mind is the biggest part of any workout - if your heads not in it it becomes tough to stay motivated. Here's some motivation for you; keep up with off-season training and while all your friends have called it after a couple runs on a deep powder day you'll still be making fresh tracks and feeling great!