In order to clean your bulb, first make sure it is dust-free. You can achieve this by using a microfibre cloth or a feather duster. Use a piece of paper towel to hold the bulb, to make sure you don’t leave any fingerstains.
After that, you can degrease the bulb by using glass cleaner or soapy water with vinegar (don’t use hot water while cleaning, the bulb may burst due to the heat). Polish the bulb with a piece of cloth so there are no drying spots and the bulb will look shiny and new!