Not punishing the child, not acting as a secondary stress factor. I think this works best with already quite matured people. This is because such people likely have much more to worry, and the sense that they are responsible for the parent's positive or negative affect from the child's own life might create more pressure too for the child him/herself.
The idea might be to give them as much freedom as possible as children often are already exhausted from school and any further pressures would be bad.