I just got done draft proofing the coop, as last week we had a storm and I noticed a few areas that needed help. I have a door that I don't use with major gaps around it. So I cut up a feed bag, used my staple gun and took care of the area. tonight when the chickens go in and I close their little door it'll get backfilled with mulch. I use the deep litter method and that puts off a good amount of heat.
Keeping the water from freezing is the biggest thing- a heated dog bowl works wonders.
A few of my girls are a bit bare in the feather area- due to molting and an over excited rooster. So I made them saddles out of fleece.
When our temps here drop below freezing I add BOSS to their diet as well as make them a warm breakfast: scrambled eggs, oatmeal, cracked corn. They really enjoy it. They really don't like to go outside if it's in the teens so I give them a pumpkin or head of lettuce to keep them entertained.
This is my first winter with chickens and it's been a learning experience.