In the Tibetan Buddhist tradition, there is a set of 59 slogans, called Lojong mind-training practices, that offer practical guidance for refining and purifying one's actions. They include the recommendations to start the day with the intention to do no harm and to end the day by reviewing our conduct to see if we've followed through.
And what if we have not? It's not an excuse for recrimination or beating ourselves up. It's possible to purify the effects of harmful actions.It starts with acknowledging the unskillful action, seeing that it has harmed us and others, and setting an intention not to repeat the behavior.
The idea here is to change habitual patterns -- anger, sarcasm, arrogance, envy -- that harm ourselves and others. We take responsibility for our behavior, acknowledging our unskillful response and not blaming the circumstances or the devil who made us do it, and see that we can choose to behave differently -- and promise (to ourselves) that we will try to do that.
Atonement, or purification practices, involve the two wings of Buddhism: wisdom and compassion. The recognition of our behavior and its effects requires wisdom, clear-seeing that is unfiltered by justification or judgment. Having recognized our behavior as harmful, we vow to change for the benefit of all beings, which is called compassion.
In Zen Buddhism, there is a formal atonement ritual. In Tibetan Buddhism, there are several purification rituals, including Vajrasattva practice. Both of those practices involve visualizing a deity who purifies the karma -- the deity is a symbol for your own inner, pure nature.
The practices don't require a deity. It's a simple reflection. The trick is to do it without getting caught up in the stories we use to justify or explain our behavior, and sometimes picturing an outside entity helps with that.
Another of the lojong slogans says: Drive all blames into one. That means that instead of blaming the weather or the traffic or the email from your new boss for your bad mood, you take responsibility for it. If someone backs into your car and dents it, you take responsibility for your reaction (but not the repair bill). Do you yell, call them names, moan about why this always happens to you? Or calmly make the calls and then move on? That's your choice, and that's what atonement or purification practice brings to light.
“We are not compelled to meditate by some outside agent, by other people, or by God. Rather, just as we are responsible for our own suffering, so are we solely responsible for our own cure. We have created the situation in which we find ourselves, and it is up to us to create the circumstances for our release.”
- Lama Thubten Yeshe, "Wisdom Energy"