If rules are consistent, results of disobeying them will be predictable. The importance of a rule is learned by consistently having it enforced. A child who is disciplined for throwing the ball in the living room on Monday but not disciplined for the same action on Tuesday is confused. By not knowing why they are disciplined one day and not the next, children don't learn the reason for rules or principles. Consistent enforcement of rules tells the child that rules are important.
Children learn values and beliefs more by examples adults set than by verbal instructions.
Screaming at children to be quiet is not effective. Ask them quietly to lower their voices. Decide what is important and what response reinforces what you are attempting to teach. Frequently the message a caregiver sends is not the message the child receives. Sometimes we communicate double messages to them.