We're in SW Virginia, so it doesn't get to negative temps or anything, but it still gets cold for birds!
It's not really cold for them. They are wearing down jackets! But they don't like wind when it's cold.
Make sure they have a place to get out of the wind, especially when they sleep.
Fresh air is good, direct wind not.
Sometimes it works well to have a solid roof, 3 solid sides of the coop, and hardware cloth on the entire front (if that front is not facing toward the prevailing wind.) When I say "solid," that can even be tarp over hardware cloth--I just mean the wind doesn't come through.
Use a heated water dish, or else replace water every morning and as needed during the day.
Typical chicken waterers have a narrow little trough, and the water has to flow through a small hole--those parts freeze fast, and then the chickens cannot get any water (even if the main part of the waterer has not frozen).
A bowl of water starts to get ice at the edges, but the middle stays thawed longer, so they can still drink. Rubber bowls make it easy to dump the ice without breaking the bowl, or you can give the chickens a fresh bowl and bring the frozen one inside to thaw.
If you worry about them needing extra calories--just add water to some chicken food to make a warm, wet mush. They seem to love it, and will happily eat enough to fill their crops. Good in the morning when they wake up, and the evening before they go to sleep. (Not required, but they like it, it does no harm and might help, and it makes the person feel better.)