Other than specialist clothing such as wet-weather gear, boots and ski clothes, a carefully selected range of ordinary clothes is often advisable. These are usually known to be comfortable and are already available. Synthetic fabrics are being used more and more as they tend to be lighter in weight, are often more robust and usually dry more quickly. Whether natural or synthetic fabrics are selected is an individual preference.
Leaders must make sure that the group members are aware of the layering principle. Several thin layers with the air trapped between them provides very efficient insulation. It also allows flexibility when adjusting clothing for variations in temperature. Beginners should be advised to take enough suitable, warm clothing, even on midsummer trips, as cold conditions can occur in any season. Very heavy woollen jumpers are rarely satisfactory, and wearing jeans can be deadly in wet weather, due to the wicking effect, which greatly increases heat loss from the body. Remind the group to have a spare set of dry clothes left in the car to travel home in.
Possibly the best advice you can give is to read lists provided, and talk to and observe others and their equipment on trips.
See Appendix 1 for clothing and equipment lists and Chapter 13 for specific equipment information about skiing and snow camping.