The Buddha introduces the topic of kamma with generosity and gratitude

"When [the Buddha] introduces the topic of kamma, he doesn’t talk about the bad things you’ve done in the past; he talks about good things. The first topic he mentions in connection with kamma is generosity. Generosity, he says, is something real. It’s a good thing to be generous. He even has you use it as a topic of focused contemplation. When things are going dry in your meditation and everything seems to come to a stop, remind yourself of the ways you’ve been generous in the past.

The other topic the Buddha uses to introduce the topic of kamma is gratitude. Think of all the people who have helped you in the past — the ones who volunteered to help without you’re doing something nice to them first. They helped you out of the goodness of their hearts. That sort of action is worth appreciating, worth emulating. You realize how much you benefited when you were fed by them or clothed by them or taught or helped in whatever way they did. And this, combined with the principle of generosity, should inspire you to do good things for other people, to pass on the help.

So when the Buddha teaches kamma, he doesn’t start with the negative side; he starts with the positive side to emphasize that that’s what you want to make the most of. As for things you’ve done in the past that were unskillful, he advises you not to get tied up in remorse about them. Remind yourself that they really were unskillful, but you can’t go back and undo what you did. Tying yourself up in knots with thoughts of guilt or remorse, however, is not going to help either. What you should do is simply resolve that you’re not going to make those mistakes again in the future. That’s all that any human being can be asked to do."

~ Thanissaro Bhikkhu "May I Be Happy"