Be a Leader: How to Change People Without Giving Offense or Arousing Resentment:
A leader's job often includes changing your people's attitudes and behavior. Some suggestions to accomplish this:
Begin with praise and honest appreciation.
Call attention to people's mistakes indirectly.
Talk about your own mistakes before criticizing the other person.
Ask questions instead of giving direct orders.
Let the other person save face.
Praise the slightest improvement and praise every improvement. Be "hearty in your approbation and lavish in your praise."
Give the other person a fine reputation to live up to.
Use encouragement. Make the fault seem easy to correct.
Make the other person happy about doing the thing you suggest.
-- Dale Carnegie