My best tip is to take steps to prevent frostbite in your chickens. This is done in three easy steps. First, make sure the air inside the coop is as dry as possible. Plenty of ventilation, clean, dry bedding, and no leaks in the roof or drinking water containers will accomplish this. Second, provide roosts that allow the birds to protect themselves from the bitter cold. Chickens are perfectly capable of protecting their most vulnerable parts (comb, wattles, and feet) as long as they have the proper roosts. Roosts should be made of wood, not metal or plastic, and should be wide enough that the bird's feet are completely covered when it is sitting. A 2x4, positioned away from drafts, with the wide side horizontal, is excellent. The chicken will settle down over it's feet, then tuck it's head under it's wing to protect it's comb and wattles from getting too cold. Lastly, don't be tempted to provide artificial heat inside the coop. It is actually harmful for your birds. Warmth inside, and freezing temps outside are a recipe for increased moisture and can even cause condensation to form on interior surfaces. Chickens are better off in natural temperatures and naturally dry winter air than they are in the warm moist air that a heated coop will provide. So, for your birds sake, give them a dry home, proper roosts, and no artificial heat, and you will help keep frostbite from being an issue.