What is the best credit mix?

Can you elaborate on what exactly is meant by "the best credit mix"? Is it a specific ratio of different types of credit accounts, such as credit cards, loans, and mortgages? Or is it more about ensuring a balance between secured and unsecured debt? Additionally, how does having a good credit mix factor into a person's overall credit score? Are there any specific strategies or tips for optimizing one's credit mix to improve their creditworthiness?