Don't criticize, condemn, or complain. Any fool can, and most do.
People tend not to blame themselves so it's futile to criticize. Puts people on defensive, strive to justify themselves, wounds pride, arouses resentment. Reward good behavior instead, try to understand, to figure out why. How would Lincoln handle this? Improve yourself instead, it's more profitable.
Give honest and sincere appreciation
"The deepest principle in human nature is the craving to be appreciated", the "desire to be important". "Hearty in my approbation and lavish in my praise"
"I shall not pass this way but once; any good, therefore, that I can do or any kindness that I can show to any human being, let me do it now. Let me not defer nor neglect it, for I shall not pass this way again."
Arouse in the other person an eager want
How can I make this person enthusiastically desire to do it? See it from their point of view.
Let others improve your idea until it's theirs
Become genuinely interested in other people
You can make more friends in 2 months becoming interested in people than in two years trying to get people interested in you
Put yourself out there for others by doing things that require time, energy, unselfishness, and thoughtfulness
Smile at someone every hour of the day
A person's name is to them the sweetest and most important sound
Be a good listener. Encourage others to talk about themselves.
Talk in terms of the other person's interests
Sincerely make the other person feel important
The only way to get the best of an argument is to avoid it
Welcome the disagreement, distrust your first instructive impression, control your temper, listen first, look for areas of agreement, be honest, promise to think over your opponent's ideas, thank opponents, postpone action to think
Show respect for other's opinions, never say, "you're wrong"
You're not right more than 75% of time, so don't expect it from others
If you're going to prove something, don't let anyone know, do it subtlety
If you're wrong, admit it quickly and emphatically.
If you know you'll be rebuked, say it about yourself, take the wind out of their sails
Begin in a friendly way
Get the other person saying "yes, yes" immediately.
Let the other person do a great deal of talking.
Let the other person feel that the idea is theirs.
Try honestly to see things from the other person's point of view
Be sympathetic with the other person's ideas and desires
If you were them you'd feel the exact same way
Appeal to the nobler motives
Dramatize your ideas
Throw down a challenge
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 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.