To clean a Honeywell humidifier, unplug it and empty its water tank and base. Clean the water tank with a white vinegar solution using a cleaning cloth, then use a scrub brush to remove mineral deposits. Wipe down the base with a cloth, and clean the filter and nozzle. Reassemble and run the humidifier with clean water to flush out any remaining vinegar. For deep cleaning, use a commercial cleaner or soak the humidifier overnight in a vinegar solution. Clean regularly to prevent buildup and ensure optimal performance.