There are many forms of karma, some can be mitigated, some have to be lived. One way to lessen your karma is to forgive those you believe have done you wrong. In doing so you free the other of a specific karmic debt to you and free yourself from the burdens of anger. Anger can cause imbalance even illness, this anger is misplaced even if the other party has done you wrong.
They are just the bringers of Karma, the karma is yours to resolve. The Universe will act on the bad actions of others bringing them universal karma for their ways, but the specific karmic debt to you is washed away through forgiveness. This is very important, to have this attitude of forgiveness of self for the karma in the first place, part of your learning experience and for others to be free of karmic debt that will only cause more suffering. Karma that can be mitigated through forgiveness is vast, but how do we get to this place of forgiveness.
Start by seeing your life in Truth, as a vessel for change and growth. Once this is accepted one can see karma as a way to ascend and become Love. Much of the suffering that takes place between people can be avoided with this attitude based on Spiritual Wisdom and Truth. To be bound by karmic debt to others brings great suffering, these debts can be made void through forgiveness. This kind of forgiveness allows for the release of your own karmic debts, as you learn to live in Loving forgiveness of others it releases you from the karma you have with others. This wisdom to turn the other cheek is old, but without the understanding of karma, action and reaction as a universal law, it goes un done.
Many think the bringers of karma deserve to be punished or banished, this is not so. If in the now the relationship is still one based on karma, forgiveness is the way through. This does not mean to befriend those that do harm to you, it does mean that you along your souls journey have done this to another and the universe is bringing it back to you to resolve. This resolution helps you to move forward in life and spiritual growth, leaving the karmic relationships behind you.
Many want revenge for wrong doings, this only keeps the karma alive. Even justice for wrong doings should be left to the universe and not you. Once you are in a place of forgiveness you can decide weather this person or persons belong in your life. This is a decision based on the now, and how they treat you. If they are unworthy of your contact it will be clear by their actions in the now.