Putting out bird houses and roosting boxes will help to keep them warm. Straw left from Fall decorating is often picked up by birds and used in trees to make roosting spaces to keep warm. Often you will see birds carrying leaves to hollows in trees to make a warm bed for the Winter night.
Simple things can help birds fatten up during the day that will help them during the cold night. Keep seed feeders filled not to the top, but 2/3 full so that they can be refilled every day or so. This way feeders always have fresh loose seeds and not frozen.. Birds go through a lot of seeds and a lot fall out. Pat down any snow below your feeder so ground feeding birds will eat the fallen seeds.
There are things from your kitchen that can be used to help your birds. Old pie tins with holes in them make perfect platform feeders for birds that are ground feeders like Cardinal, Juncos, Towhee, Wren, Sparrow, and Doves. I have nailed two to my deck rail and filled both at times with sunflowers seeds and bits of fruit. Bread crumbs and bread used to wipe out a skillet after frying bacon works well in those pans, too. The fat is good for birds and is much like suit which is made from rendered beef fat with, seed, dried fruit and grain added.
Water in Winter is important for birds. But, keeping water for your birds is tricky. In no time it turns to ice unless you purchase a water heater. One most often used for a bird bath. Last year I purchased two very large dog water bowls. The type used for a big dog and made of a soft plastic. I fill one and when it turned to ice I turn it over and fill the second one. The ice slides out of the first one and I'm ready to go. I do my water changing in the morning when the birds are around and active.
Bird watching is the second favourite hobby in the world - only second to gardening. So put your feeders, houses and pie pans near a window. Grab a cup of tea and a chair and watch the birds of Winter.