1. Take responsibility. Say, “I was wrong.” (Don’t say “mistakes were made” or “it didn’t turn out the way I had anticipated” or any other version that deflects or minimizes your personal contribution). Offer a brief explanation, but do not make excuses. Acknowledge that your error had a negative impact on others, and be willing to really listen, without defensiveness, to others’ recounting of that impact. Do not interrupt. Apologize.
2. Address what you need to do right now. Taking responsibility is critical, as is taking action. This is core to crisis communication, even if your mistake doesn’t constitute a major crisis. Tell others what you are doing right now to remedy the mistake, and distinguish between the parts that can be fixed, and those that can’t. Include what you are doing to address the substantive impact (money, time, processes, etc.) and well as the relational impact (feelings, reputation, trust, etc.) of having been wrong. Be open to feedback about what you’re doing. Over-communicate your plans.
3. Share what you will do differently next time. Being wrong is messy. Being wrong without self-reflection is irresponsible, even if you hate self-reflection. Take some time to think about what your contribution was to this situation, and identify how others contributed as well. (Try to stay away from using words like “fault” or “blame” — which tend to put people on the defensive.) Then tell those impacted by your error what you’ve learned about yourself, and what you’re going to do differently in the future. For example, you might recognize that you tend to dismiss the input of someone you don’t see eye-to-eye with, and that in the future, you’re going to actively engage her, and consider her perspective. Ask for help where you need it. And ask others to give you frequent feedback down the road on the commitments you’re making.

Continual reminders to myself to do better.