Avoid temptations to blame or attack.
Casting blame or antagonizing others is more likely to make them defensive, or push them to fight back, rather than encouraging them to really listen to you or to see your point of view.
Speak for yourself, and let others speak for themselves.
Avoid assuming that you know why the other party behaved as he/she did. Instead, tell him/her how the behavior looked from your perspective, and how it impacted your behavior. Let the other person tell you what was going on from his/her perspective.
Show that you are listening
Mediation requires listening. Each side needs to be heard. Listening should also be expressed in body language and facial expressions.
Talk it all through
Talk out everything that is important to you, whether or not it's significant to others.
Work toward a solution
Try to focus on solutions, not blame. The goal is to resolve the conflict and prevent similar ones from happening in the future.