If your dog is a shorthair breed think about getting a warm coat or sweater with a high collar.  Look for a garment that covers the dog from the base of the tail to the top of the animal to the belly to cover underneath.

Never shave your dog down to the skin in the winter.  Longer hair in the winter reqires more frequent brushing due to dry winter air and static electricity and when you bath your dog make sure that the animal is completely dry before taking it outside.

Puppies especially do not tolerate the cold as well as adult dogs so in cold weather take them outside only long enough so they can relieve themselves.