You have a Karma bank account. Without you ever knowing, each good deed is deposited into your Karma account and each bad deed makes an automatic withdrawl. All the good and bad deeds over your lifetime have been building or draining your Karma bank account. If bad deeds have caused your Karma acount to become overdrawn, there is plenty of time to make good-deed deposits to top it up.
Unselfish acts are considered some of the best actions you can take to top up your Karma bank account. Instead of the pain of Karma teaching you how to act properly and good, you can learn on your own through reading, study of correct behavior of others whether through biographies or watching good people doing good deeds, by applying the law of cause and effect, and by acquiring wisdom in any other possible way. Doctrine reassures us that unselfishness is a very powerful action with many benefits associated to it.
Rule: do plenty of unselfish, kind acts, to make others winners, to help cancel the bad Karma in your Karma bank account.