Be considerate of others. Seems like that would go without saying, but it is often the missing link in troubled relationships.
Say “Thank You” to those to whom thanks is due. People love to hear those words, but more than that, when they do hear them, their regard for those who spoke them goes up.
Overcome evil with good. It is a very Christ-like action to be kind to those who are not kind to you. If the other person has any heart at all, it will make a strong impression that will probably pay big dividends in your future dealings.
Leave vengeance to God. In Romans 12, God says that vengeance is His, and that He will repay. Do you trust God to take you to heaven when you die? Then, can you not trust to take care of this little matter?