There are some vaccinations available that you can give your chickens, but if you bought them from a hatchery check with them first. Some hatcheries vaccinate chicks before sending them off.
For chicks you can feed them medicated chick starter. That helps prevent coccidiocis. I give my chickens some Apple Cider Vinegar (ACV) in their drink water. It gives them a general health boost, helps prevent pasty butt in chicks and also helps prevent coccidiocis. The ratio is 4-5 tablespoons to a gallon water. Give it to them for a week, then clean water for 3 weeks, then ACV water for a week...
You could also deworm your chickens when they are a month old. Most people deworm every 6 months as a preventative measure, but you should deworm immediately if you see evidence of worms in their poop.
Also dust the chickens and their pens regularly for mites and lice. Food grade Diatomateous Earth (DE) is safe to use and works very well.
Apart form that ensure good coop hygiene. Clean and dust the coop and perches regularly, don't let the poop build up too much in the run and make sure they always have fresh water available.