Easy! You just don't talk about things that others do not need to know about! Interviewers need to hear that maintaining confidentiality is easy for you. Share that maintaining confidentiality is of the utmost importance, and you just don't share things that others do not need to know about. Additionally, share that you ensure papers are turned over on your desk when you are away to add protection from wandering eyes. Mention if you lock your filing cabinet drawers. Discuss if you lock your office door each night. And, mention if you use a screen cover to keep others from being able to read your computer monitor.