Consider sun, wind and snow conditions, and suitability of terrain when choosing a site. Establish emergency procedures and explain those procedures to the students. Teach skills in proper progression. Discuss recognizing and treating frostbite and hypothermia with the students. Have students check to be sure boots are secure in bindings.
Ski poles have sharp tips.
Caution students about their use, especially when working close to others. Be aware of students with a history of asthma and other respiratory problems. Use a buddy system. Make parents aware of off-campus activities. Clearly outline duties of supervisors, including supervisors of small groups of students.