Frame your mindset:
You may feel angry, stressed, upset, irritated but channelize your mind in a positive way. For example, You are not going to say NO to your boss, you are offering an alternative solution. Always believe that there is a creative way to solve the problems.
Empathize the Counterpart:
Prepare and try to answer a list of questions from your counterpart’s view. Behind every move, there should be a rationale element which you are not aware.
Prepare Well Enough :
You won’t know ahead what is going to happen during the conversation. But still prepare the list of question you want to get clarified off . You may talk just of ten minutes, but the preparation will have huge payoff.
Talk your feelings, emotions to a trusted person. Never pile up your emotions. If you pile up, it will spill over. So it’s better to talk it over before talking it over to your counterpart.
Source : https://hbr.org/2016/04/how-to-mentally-prepare-for-a-difficult-conversation