Keep the water, and waterers clean. Don't let feed get old, or moldy. At least once a week, pick up a few of your birds, and check them over for lice/mites weight loss, etc. The next week, pick different birds. Keep flooring, and nesting materials fresh. Clean up the roosts as needed with soap and water. I spray my coop with permethrin at least once a year, and dust my chickens once a year, unless there is evidence of a problem, then I treat accordingly. I worm at least 2 times a year, but it's warmer here than up north, however, they have worms up north too. Pay attention to their combs. When they're pale, or very lackluster it is usually a sign that they need worming. During molt, I boost the protein some, and make sure to give canned cat food, since they need a bit of animal protein, not just vegetable protein which is what is in most feeds.