Listen for facts and emotions. Compose your message carefully. Consider your goals and the goals of the other person. If you make a mistake, admit it and do your best to recover from it. The sooner you deal with negative feelings, the easier it is resolve things and get back 'on track' to achieve positive results.
Cooperation is more valuable than destructive competition.
At times emotions are so strong that it is difficult to say things in a constructive way. At these times choose whether to 'cool off' and take a 'timeout' or to clear the air and allow the other person to know how you feel. This is a judgment call and experience is the best teacher. Be gentle with yourself and others. We tend to judge ourselves by our intentions and others by their behavior.