Using privacy filters on monitors is the most direct way to reduce the risk of shoulder surfing, as these filters narrow the viewing angle of a screen, making it harder for individuals to see the content unless they are directly in front of it. Implementing a clean desk policy and promoting the use of secure lock screens are good security practices, but they do not protect against shoulder surfing of an active monitor. Biometric authentication is also helpful for securing access to devices but does not prevent shoulder surfing once the user is authenticated and using the device.