[header] How to clean a bathroom fan [title] Turn off the power. [step] Before you do anything else, ensure that the fan is turned off and cannot turn back on until you are finished cleaning it. Most models will have a plug that is located directly behind the cover. 
You could remove the cover first and unplug the fan, but just to be safe, go and temporarily pull the breaker for your bathroom. The fan is now safe to work on.