Simply empty your Glow Dreaming out fill with warm/hot water from the tap and add one tablespoon of white vinegar.
Let sit for 30mins then empty and dry out with a soft cloth or paper towel. (Just be careful of the sensor in the middle of the base).
You can also wash the lid(s) being careful of the smaller inner lid as it has a fragile little piece of plastic holding it together. (You can remove this being very careful but not necessary). Clean the lid(s) with warm soapy water and let them air dry.
You can use other oils in the Glow as long as they are good quality and not synthetic as they can damage the unit.