Closing unused ports on a server helps to minimize the attack surface by ensuring that only necessary network services are accessible. This effectively reduces the number of entry points available to an attacker. Keeping unused ports open does not contribute to security, as it unnecessarily exposes the server to potential exploitation. Switching port numbers can obscure services but does not decrease the attack surface. Using complex passwords is good practice for account security but does not pertain to network services and port/protocol security.