1.) Light it up
If you want to have them lay all year you will need to supplement their light. They need between 14-16 hours of light to lay. If they don't get this they will molt and stop laying. Some people give their chickens a break but that isn't usually the case for working hens.
2.) Give them something to do
In the summer they have plenty to dig up, run after and keep them busy. So, in the inter months your flock might get a little bored and they might end up pecking at eat other.. Give them something to do. Give them a pumpkin, cabbage head, squash or block to pick apart instead.
Chickens are amazing compost turners. Add a compost pile to your chicken run and let them turn the soil for you.
Depending on your climate you may not need a heater and truthfully heaters can be a safety hazard. A hen's body temperature is 106° F and their feathers are a natural insulator. The hens will roost together and will keep each other warm. But there may be times that you need to give them a little more warmth. If you use the deep bedding method (adding more shavings on top of the other shavings) it will add to the insulation and increased heat due to the composting materials.
4.) Ventilation without drafts
Although on very cold nights you might want the option to close up the coop, it is better to have the ventilation and air circulation in your coop. All the decomposing matter and build up can cause an overwhelming amount of ammonia build up in your coop. Also depending on the types of chickens you raise they have adapted (or have been breed) to be cold hardy). Installing high windows that open and close (and have predator proof screen on them) are a great option for this type of ventilation.
5.) A change of scenery
Depending on your type of greenhouse you could also move the chickens into an unused greenhouse or chicken tractor for some portion of the winter. They would be protected from the elements. They will dig up the ground and fertilize at the same time. Just make sure it doesn't get too hot. At the same time you could add a cover crop to the chicken run which will supply them food in the spring and summer.
Chickens will run around in most weather. But if you have deep snow for long periods of time you may want to add some straw or hay to cover the snow so it is easier for them to move around.
7.) A room with a view
Sometimes it's nice to get a different view, who doesn't like a nice view. Creating some different spots to roost will give your chickens many options to Your chickens may enjoy a different spot to roost if you live in a climate where you get deep snow.
Keep a heated waterer so that the hens have access to fresh water that isn't frozen. It's important to have available and clean water.
9.) Time to collect the eggs
Collect the eggs in the morning and evening so that they don't freeze. You'll know that the egg has frozen because it expands and cracks.
10.) Keep the coop dry
Hens will spend more itme in the coop during the winter. Stop moisture and leaks so that they have a dry environment to roost.
11.) Keep out unwanted visitors
The winter brings other hungry animals. You don't want them in the coop and transferring diseases to your flock. Block up small holes and areas that could bring in unwanted guests.
12.) Dust bath
Chickens give themselves dust baths to keep down mites and other unwanted pests. In the winter it's harder to find a patch of dry ground to give yourself a nice dust bath. So, adding one to your coop is a nice way for chickens to keep up their hygiene and also give them something to do. Add some dirt and sand to a large container and add it to their coop in a dry spot.