I use a toothbrush with a bit of cleaner. Either a very mild kitchen cleaner, or if real stubborn, sometimes Mean Green. Then I quickly wipe it down with paper towel (that allows me to see how much dirt came up) Not a complete cleaning, but I'm not going to take it completely off and submerge it in water. (I work on EMs and would require lots of de-soldering from bulb sockets to do that) Sometimes I will give certain areas special attention if obvious build up of dirt.