Explain why it happened (with sorry early in the explanation.) Explain how your decision making has now changed or will change so it doesn't happen again. Don'

Explain why it happened (with sorry early in the explanation.) Explain how your decision making has now changed or will change so it doesn't happen again. Don't get the scope wrong - if you are only going to make such a minor change that lots of almost-identical incidents will still happen in future, don't bother. Conversely, if you make quite exaggerated claims about the change you will make, also maybe don't bother. If in contrast to a real apology that promises change, your "apology" is really a backhanded promise that it'll all happen again and probably soon; don't expect that to be gracefully accepted.