1. Avoid criticizing, condemning, or complaining.
"Any fool can criticize, condemn, and complain - and most fools do," Carnegie writes. "But it takes character and self-control to be understanding and forgiving."
Anyone in a leadership position should acknowledge when a subordinate is not meeting expectations or when a competitor's approach is inferior to their own, but do so in a way that acknowledges what is working, avoiding resentment and encouraging improvement.
2. Praise others' achievements.
"Abilities wither under criticism; they blossom under encouragement," Carnegie wrote. Be lavish with praise, but only in a genuine way, he advised.
"Remember, we all crave appreciation and recognition, and will do almost anything to get it," he said. "But nobody wants insincerity. Nobody wants flattery."
3. Be empathetic.
Carnegie writes that "the only way on earth to influence other people is to talk about what they want and show them how to get it."
He refers to a quote by Henry Ford: "If there is any one secret of success, it lies in the ability to get the other person's point of view and see things from that person's angle as well as from your own."
Steel magnate Charles Schwab claimed his smile was worth a million bucks.
"And he was probably understating the truth," Carnegie writes. "For Schwab's personality, his charm, his ability to make people like him, were almost wholly responsible for his extraordinary success; and one of the most delightful factors in his personality was his captivating smile."
5. Encourage people to talk about themselves.
Most people loosen up even in tense situations if they start talking about what they know. Namely, themselves.
Listening closely to someone "is one of the highest compliments we can pay anyone," Carnegie writes.
6. Know when to use suggestions instead of direct orders.
Carnegie learned that the industrialist Owen D. Young, rather than barking commands to his subordinates, would lead them along with suggestions ("You might consider this...") or questions ("Do you think this would work?").
"He always gave people the opportunity to do things themselves; he never told his assistants to do things; he let them do them, let them learn from their mistakes," Carnegie wrote.
7. Acknowledge your own mistakes.
The best leaders, Carnegie said, do not lionize themselves, appearing as if they were flawless.
"Admitting one's own mistakes - even when one hasn't corrected them - can help convince somebody to change his behavior," Carnegie wrote.
8. Respect others' dignity.
Whether leaders are giving employees a demotion or letting them go, they need to recognize that person's dignity and not humiliate them, Carnegie said.
And even from a practical standpoint, it's in a leader's favor to remain on good terms with an employee who didn't work out, since it's possible they will cross paths again, and a single irate former employee can have motivation to ruin their former boss' reputation.
9. Don't try 'winning' an argument.
Even if you manage to tear apart someone else's argument, you don't actually achieve anything. Carnegie cites the old saying, "A man convinced against his will/Is of the same opinion still."
If you're looking to actually persuade somebody, avoid an argument in the first place.
10. Be friendly, no matter how angry the other person may be.
It's human nature to meet aggression with aggression. But if you take the high road and try to persuade someone while maintaining a smile and showing appreciation for their situation, you'll be surprised what you can achieve.
11. Reach common ground as soon as possible.
"Begin by emphasizing - and keep on emphasizing - the things on which you agree," Carnegie writes. "Keep emphasizing, if possible, that you are both striving for the same end and that your only difference is one of method and not of purpose."
12. Get others to think your conclusion is their own.
No one can be forced to truly believe something. That's why the most persuasive people know the power of suggestions over demands.
Plant a seed and when that's blossomed, avoid the urge to take credit for it.