The outer layer should protect the runner from wind, rain, or snow. Wear fabrics that insulate and wick moisture away. Fabrics made of wool and polypropylene are good. Avoid wearing cotton because it retains moisture. Protect special body parts like your head, face, hands, and feet.
Mittens are better than gloves.
Cover the head with a wool cap. Shield the face with a scarf or high collar. Wear socks that retain heat and wick moisture away. Drink plenty of fluids. Do not drink alcohol before or during a workout, because it makes the body lose heat faster.