Autism is a very complex spectrum of behaviors and symptoms and it's risky to generalize. But here are some things to think about.
Ritual and consistency can become vitally important to autistic students. From the beginning, pay attention to how you structure and organize your class. Little things that a "normal" student might not even notice, such as how you describe things, where you stand, even which ski the student puts on first, become very important. Breaking established patterns can have bad consequences. Be aware of the rituals that the student creates. For example, if the first time you go up a chairlift you are on chair number 34, that may become the student's only chair. I've seen an autistic teenager wait at the bottom for "his" chair to come down before he would load. Luckily it was a very short chairlift.
Many autistic people have a difficult time with "sensory overload". Sounds, light, movement, can all be very confusing to them. Although you can't always avoid these, be aware of the effect they can have. On the positive side, though, nature, trees, sunshine, a light breeze, can often have a profoundly calming effect on students who might be very nervous and agitated in an indoor environment.
Autistic kids very often are not hampered by fear of movement. They will often become totally engrossed in learning movement patterns. This can be both good and bad, for obvious reasons. You have to be extra aware of safety. But the student may be exceptionally able to imitate a good demonstration or to repeat a movement once he or she has experienced it.
Many yourger autistic kids have a very hard time with physical contact. The big hug that you might give another seven year old at the end of a good straight run down the hill could result in an almost violent avoidance on the part of an autistic child. Ask the parent of guardian about this.
Take your time. Don't expect quick results, but don't be surprised by the results you CAN get if you're patient, consistent, and thoughtful. Have fun.