Try to pick an example that is not a critical area for the role you are interviewing for. See if you can come up with a learning that is relevant to the new role. For example, you might be not being good at delegating when you were first appointed as a manager. You could build your example around these points:
Other mistakes you could speak about include miscommunications, misunderstandings, missed deadlines or errors made. Avoid saying you don't make mistakes or that you can't recall any.