The minute these signs are spotted, get the victim to shelter of some kind and wrap him or her in warm blankets or a sleeping bag. Ideally another member of the party should get in the sleeping bag with the victim for added warmth. If practical, it's best for both people to be unclothed, but if clothing remains on, it must be dry. High-energy food and hot drinks also aid recovery. To avoid hypothermia, always carry warm, dry clothing, avoid immersion or exposure to cold water or rain, and keep energy levels up by eating high-calorie foods like trail mix.
Frostbite is caused by exposure to extreme cold for a prolonged period of time.
Frostbite victims should be taken into a warm place as soon as possible, and wet clothing should be removed. Do not rub the frostbitten area, as this may cause permanent damage to the tissues. When the area begins to thaw, the victim should exercise it, to stimulate blood circulation. If bleeding or other complications develop, get to a doctor as soon as possible. Resources Hypothermia and Cold Weather Injuries For information on how your body regulates its temperature and for a complete discussion of symptoms and treatment, see this page maintained by Princeton University's Outdoor Action program.