First of all, dress in layers.  Start with thermal long johns, heavy cotton t-shirt, then heavy weight cotton long-sleeved shirt, cotton trousers, double socks, one lighter and one heavier.  When working outdoors, I wear a heavy CarHartt insulated jacket, and then an insulated CarHartt overall over the jacket and trousers.  I wear insulated chopper mittens.  I wear Rockies insulated boots, and a heavy duty rabbit fur-lined bomber cap, over a baseball type cap.  I do not like hoods, as they do not seem warm enough for me.  I cannot wear wool next to my skin, as it is irritating. Dressed like this, I can be out in 30 below temps for quite a long time.  I never leave home without taking along insulated overalls and boots and heavy cap, in the winter.