The best practice for password security from the options provided is:
changing passwords often
While keeping passwords unique for different sites is also critical (implying not using the same password for many sites), the most relevant option listed here focuses on the practice of changing passwords regularly to enhance security. However, it's important to note that simply changing passwords often without other security practices (like using strong, unique passwords) may not be sufficient. Always aim to use complex, unique passwords for different accounts and consider using a password manager for better organization and security.