Second to have a mirror on their stand every day. Not looking down, the stand needs to be all the way up to the level of their chin. Head should be in a natural straight position. Headjoint comes to you, not you to HJ. Agree with whoever said you need to practice on HJ all summer. You will have to place the HJ for them for the first few weeks? To form the embouchure, have them pretend they're spitting a grain of rice, or blowing on hot soup. Have they been tested already? If they have a tear drop upper lip or weak facial muscles it will make it very difficult for them to form the embouchure.