In my opinion, keeping a closed flock and providing a balanced diet, adequate clean water, and a dry environment are the most important things you can do to keep a healthy flock.
If you have a history of a specific disease in your flock, then you should of course take the required precautions based in that specific disease. That may or may not include a vaccination. Personally, I treat for known problems and don't treat when I don't have a specific reason to treat.
Some people worm their chickens on a regular schedule, once or twice a year usually. Some of us only worm when we see a specific problem and treat for that specific worm. Different worms require different worming techniques or medications.
Before I got chickens, I spoke to my county extension agent, in the phone book under county government. He put me in touch with a university professor that teaches courses on chicken diseases and treatment. He also is on the regional task force that investigates chicken disease in this area. After discussing disease history in this county and how I was going to manage my chickens (no shows or swaps, do not bring in new chickens other than day old chicks from hatcheries or hatch the eggs myself, no chickens over three years old to be kept) I decided to not vaccinate for anything. That is based on my county and my situation. The recommendations for your area or the way you plan to manage your chickens may give you a different answer.