Layer your clothing. Many layers of thin clothing are warmer than one bulky layer. Air spaces trap body warmth close to the skin, insulating the body against the cold. Wear 2 or 3 pairs of socks instead of 1 heavy pair, for example, and wear roomy shoes. Don't drink alcohol or smoke cigarettes.
Alcohol causes blood to lose heat quickly.
Smoking slows down blood circulation to the extremities. Stay indoors as much as possible when it is very cold and windy. When you are outside, shield your face, etc. from the wind. If victim is not breathing but has pulse, do rescue breathing. Get victim out of the cold and into a warm place.