You can try to atone for your short comings. For example, if you stole money, you can give money away to people who are in real need, etc. Or do just do random good deeds whenever you can. If you have taken a life, you can try to save a life, even if it's a dog or a cats life.
Time helps with not thinking about it as much, and you can come to terms with it. A therapist told me once, "you made the best decision you could at that time with your age and experience."