"Thanks for your opinion.... I'll think about it.... Let me get back to you." Any of these statements allow you to not have to make a snap decision or disagree outright.
"Is this a good time for you?" This question before launching into a discussion acknowledges respect for the other person's time.
"Do you want my thoughts?" Ms. Puhn recommends this one for teenagers, emphasizing that it is important to be willing to hold your tongue if they say 'no'.
"Why don't we get the facts?" Often people fight over things that can easily be determined with a little research. And if you prove to be right, it is most helpful to abstain from overemphasizing that point.
"I need your help. Can you please...?" People like to help, and most are not mind readers, so ask specifically for what you need and be willing to negotiate.
"I'm sorry you're upset." Acknowledging the other person's feelings lets them know you are attending to them.
Awareness of how you present yourself regarding tone of voice and body language is important to facilitate harmonious interactions. One of Stephan Covey's "Seven Habits" is to 'start with the end in mind', so staying clear with yourself on the intention to have a positive interaction can keep your part of the conversation on track. It can also be helpful to ask for more information and discuss expectations to avoid future misunderstandings. And if you do make a commitment to get back to the person at a later time, be sure to follow through.
Psychologist Dorothy Mandel suggests emphasizing collaboration to facilitate a move towards resolution. She utilizes phrases like "How do you think we should handle this?" to invite a sense of connectedness and shared purpose. Verbally reaffirming your common goals can be helpful in supporting that sense of shared effort.
If things do take a wrong turn, one of my favorite escalation stoppers is a technique called "fogging". To fog, you agree with whatever part of a negative statement you can honestly validate, even if it invokes a "sometimes" clause. So if someone tells you that you are a clumsy fool, a fogging statement might be, "You are right, sometimes I am clumsy." We all have our less than graceful moments and owning one piece of the statement might give the other person pause and let them know that you are listening to what they say.
Keeping the peace in our own relationships reduces personal stress and increases enjoyment of day to day living. If Rupert Sheldrake's theories on morphic fields are valid, it also makes contributions to overall harmony on the planet. And we can always use more of that.