Below is simply from my experience. Hopefully, it helps those new to poultry.
Coop/run—Birds need access to fresh air and shelter. Crowded birds are stressed and susceptible to disease & injury from one another. Make the coop/run tall enough that you don't crouch to clean. A sore back will not be incentive to clean coop! Predator control--housing should be predator proof. Chickens are on the menu of MANY animals. Prepare to deter hawks, neighborhood dogs/cats, owls, coyotes, fox, skunk, raccoons, etc. Use heavier gauge wire than "chicken wire". Ensure top, bottom, sides and door entrance won't let a determined, strong predator in. Raccoons will pull birds thru wire mesh in which they can fit their paws. Changing out the coop litter every quarter or more helps the birds respiratory system (particularly when shut in during winter). If you have a low # of birds, less litter changing is ok. I use deeper wood shavings in winter than summer. I use playsand in the run for hens to dig in to cool in summer or dust bathe. Also easy to rake and clean out manure.
Extra heat in coop—If temperatures get to single digits I add a Sweeter Heater rather than heat lamp. The Heater is placed where the birds access it if they choose but not under roosts. Bantams suffer in cold more than large fowl. Keeping moisture from forming in the coop prevents frostbite & helps health so encourage ventilation with windows or wire grates so you may adjust as needed.
Water—Always have clean water available. I use the galvanized waterers in winter on top of a metal heated base. In non freezing weather, I change to a large plastic waterer. Once in while I add a tablespoon or 2 of a raw vinegar (Bragg’s brand) only to the PLASTIC waterer. Vinegar will react if put in galvanized metal. I think the addition of the particular vinegar has helped prevent egg binding in the hens.
Feed—I found a higher % protein as it works better for my silkies & bantam cochins (some disagree with high protein). I use a 26% protein Manna Pro Gamebird breeder/starter. The silkies especially showed better reproductive results--# of eggs, egg integrity, chick survival. I feed the 26% to any breeding birds, growing birds under 9 months and during winter month to all ages. I feed a lessor protein feed during warm summer months to some animals. I supplement winter feed on cold days/night with sunflower seeds, cracked corn, or scratch. These feeds with higher fat content help birds during freezing temperatures. All year, I feed bananas, watermelon, cantaloupe, cooked squashes (acorn, butternut) or pumpkin every week or so. The red orange vegies have high vitamin A content which a vet recommended for respiratory health. The birds have the run of our backyard when I am home. But I still provide lawn chairs or places for them to duck under when hawks dive bomb. We use no weed killer or any chemicals on our lawn or garden.
Lice/mites/worms--I use various dog & cat sprays from Petco/Petsmart to treat lice/mites every quarter. Or more often if I see infestation. Spray under chin, under each wing, under vent and if a silkie...in the crest. Wild birds carry infestation so best to keep poultry & feed separated from wild. I use a flaxseed worming powder from McMurray hatchery 2-3x a year mixed into the adults feed.
National Poultry Improvement Program (NPIP)--flock health information