How to prepare body for ski/snowboard season?

Start with basic exercises of walking and riding a bike, chase some fast girls, swim, dance. Learn to balance on one foot with your eyes closed then on the other foot. This schedule should be followed for 2-3 weeks at least and this is a daily ritual. It should get you in good enough shape to ski beginner slopes without serious injuries. Take a series of lessons from a qualified professional instructor.

I am an expert skier, and before ski season, I always do tons of wall sits (squatting with your back against the wall for a certain amount of time), I do thousands of squats, and If you race, It always helps to do some weight training. Also, before you go to the mountains I would recommend drinking a few gallons of water in the days leading up to when you go. Also make sure to carb up the day before so you can give your body plenty of fuel. Hope this helps!

Air squats, jump rope, and core exercises are how I keep myself up for skiing. And of course, actual skiing too :)