There are some things that you can do to prevent diseases, but they're not 100% fail-proof.
- Don't ever wear shoes from a friend's farm or a fair or anything like that into where your chickens live. Disinfect your shoes if you go somewhere that has poultry or farm animals. you can spray Clorox bleach on the soles and wipe down your shoes with Clorox wipes.
- If you are introducing new birds make sure that they are not close to your older birds for a few weeks so that you can make sure they are disease-free.
- clean your animals feeders and waterers weekly. You can use Dawn dish soap and white vinegar, let them soak for a bit.
- Make sure your animals have adequate space in the coop and in their run
- do not put wild bird feeders anywhere near your birds and if you have free range birds, do not keep any bird feeders at all because wild birds carry lots of diseases.
- clean your coop regularly. It all depends on how many birds you have, many do it every couple days or once a week.
- give your birds vitamins and minerals, nutrition is a huge thing to keep their immune systems strong
- I add apple cider vinegar into all my waterers, it's a tablespoon per gallon. This helps keep algae and other things from building up in the waterers on hot or damp days.
What breeds do you have? Are you medicating the chicks when you get them? Where are you buying your chicks from? How big is your run and your coop? How many chickens do you have? When your chickens get sick, do you medicate them with antibiotics? Did anyone have animals on your property before you resided there (sometimes the diseases can come from animals that previously live there because some of the diseases that you mention do not go away for a length of time)? What do you use in the coop as a bedding? How often are you cleaning your coop and the yard that the chickens live in?