What makes a school policy likely to be effective?

If it is promoted and adhered to be all staff members and the rule of the policy us followed ie if children required to wear no jewellery. Then if teachers see it on children to ask them to remove it., confiscated it. For there to be a punishment or sanction on people who don't follow it to discourage others from breaking the policy. If the policy has been agreed by interested parties ie the governor's and parents. Therefore it is given backing by those in power Tec and encouraging and influencing children to follow it. Clear guidelines.