Pretend you're sitting in a chair while leaning against a wall. Also take something the size of a large detergant box, place it on the ground and jump sideways back and forth across the box. Biking, running, rowing, etc. Second, general leg, shoulder, and arm exercises.
Legs are obvious.
You need to start slow. I'd suggest starting with slow running or jogging to build up your aerobics, then check out a local gym and ask for some suggestions there. The single best exercise for skiing is running up stairs. Otherwise basic overall fitness should be enough. I've found that a good, solid combination of aerobic and anaerobic exercise helps me the best.