Forgiveness is such a huge topic and mitzvah in Judaism and in the practice of making peace that an entire holiday, Yom Kippur, the Day of Atonement, is devoted to it. In preparation for Yom Kippur, you are to call each person you have interacted with over the past year and say, "If I have done anything this year to offend you, please forgive me." And if the person has done anything to offend you, you are to forgive that person as well. If the person refuses to forgive you, you are told to ask three times. If your third attempt is rejected, you are considered to be forgiven by God.
This practice needs to be done not just once a year but on a regular basis, especially with members of your family.— Brenda Shoshanna, Jewish Dharma