1. you want people to hear your opinion so make sure you practice what you preach. listen carefully to the other person and accept that he or she might be flexible and open-minded, willing to apologise, forgive and move on.
2. before you start discussing the problem, cool off count to 10, take a deep breath and imagine a relaxing place. then, say, what's really bothering you. while doing that, watch how you express yourself. don't blame or accuse. share how you feel by using "i" statements.