One thing that can help us in our quest for spiritual enlightenment is to get rid of some of the negative karma  we have. All of us have some — we have all done things we shouldn't have —  so we should do what we can to counter it. If we have harmed or offended another person, the best thing is to go to that person, apologize, and ask for forgiveness. 
    For a number or reasons, that may not be possible. Maybe the person you harmed has moved, died, or refuses to talk to you, even though the offense may have happened years ago. There are still things you can do to help reduce negative karma in those cases. 
    First, you have to try to remember those who have offended or harmed you in some way and forgive them. If you can't, or are unwilling, to go to those persons and tell them you forgive them, you can at least send thoughts of forgiveness to them. You can also send thoughts of love to those you have offended or harmed and mentally ask them to forgive you. And then you can make an effort to counter your past negative behavior with some positive behavior in the present. If you robbed someone in the past, and cannot repay that person directly, then donate the money to an appropriate charity, one that person would probably have supported. If you harmed someone by spreading rumors about that person, you can tell your kids, or teach other kids  to never spread rumors. If you insulted some person because he was poor, volunteer to work at a soup kitchen. I could give several more examples, but I think that's enough to give you the idea.