I have kind of mixed feelings about the first piece of advice from Jay. In my experience, some people need to actually think less about the "bad" they have done to others, because they will exaggerate things and it will end up haunting them. It can turn them into a person who is afraid of hurting other people's feelings. This then means that the person is less assertive, and people just walk all over them.
However, on the other hand, there are some people who think they are the best things since sliced bread, who can do no wrong. They are the ones who need to be more humble and think about how their actions have hurt others.