I don't do a all too much free skiing, so other people probably know way better than me. But, speaking from workout experience and being a human physiology major, the muscles you'll use most will be leg muscles, trunk muscles, core muscles. A lot of squat exercises, Front squats, back squats, overhead. List goes on. Lunges, multiple varieties, calf strengthening exercises, and any other leg exercises you may think of. An EXTREMELY important part is to train each segment equally, and remain flexible. Both of these will help prevent injury. For core, plenty of ab exercises, so many I won't even start to list. Lower back and obliques need to be trained just as much. Planks, reverse crunches, deadlifts, all that. Also, Olympic lifts such as cleans, deadlifts, snatches, all of that are excellent. Will help maintain and build upper body strength, while also building core and legs. Honestly, I can't just tell you a good workout to jump into, you need to figure out what exercises tailor toward your needs, your fitness level, and your available time. Research some exercises that will work the areas you need, tailor your workout to your fitness level, and adjust for amount of time you have. Before and after every lift make sure to do a good stretch, and maintain cardio in some way as well. Diet is also very important. I know this post is vague, but this is why knowledge of lifting/personal Training/physiology is very helpful in designing a routine. If you can afford it get a personal trainer, and they will definitely get you on the right track.