Do to others as you would have them do unto you.

or even better (Luke 6:40-42)

No disciple is superior to the teacher; but when fully trained, every disciple will be like his teacher.

Why do you notice the splinter in your brother's eye, but do not perceive the wooden beam in your own?

How can you say to your brother, 'Brother, let me remove that splinter in your eye,' when you do not even notice the wooden beam in your own eye? You hypocrite! Remove the wooden beam from your eye first; then you will see clearly to remove the splinter in your brother's eye.