One of the simplest ways of reducing tension in a difficult conversation is to control the tone with a couple of well-placed sentences which will appeal to the persons natural desire to be heard and understood. Saying to an angry person "I can hear this is important to you" or to a sad person "this must be difficult for you" will provide instant empathy and enable you to get to the point of the conversation much sooner. Adding in "please take your time" or "I'm listening" will counter-intuitively speed up the conversation as a rapport is built and the person becomes much calmer.