Always keep the promise. Never promise things that you can't do - or at least don't make this a habit. If you say you are going out with a friend and the conflict occurs, explain the situation and believe that the friendship will be strong enough to overcome all challenges. If you can't go, give the person a gift and say sorry. No one is perfect, and it's okay if your appointments are rare, but don't make it a regular occurrence. Otherwise, you will be deemed unreliable because you cannot keep your promise to your friends. [1]
When making a serious promise, look into the friend's eyes and speak slowly to show his honesty, not just promise. Don't break those promises, because that friend will be hurt. This action may also end the friendship.