To clean a 3.5 mm headphone jack, it is important to exercise caution since it is a delicate part of electronic devices. One method is using compressed air or an air blower to remove any dust or debris that might have accumulated inside the jack without inserting anything into it physically. Another option is using a cotton swab lightly moistened with rubbing alcohol and gently swiping around the edges of the jack to remove any dirt or residue built up over time. However, when cleaning, it's crucial never to apply excessive force or liquid directly into the jack since this could damage both the jack and the device.