The ones that have a color finish or anodizing along with a simple switch, soap and water. The ones that don't have paint or anodizing, or those with sealed tactile switches I use a cotton cloth and Hoppes #9 and then again with a damp paper towel to remove any excess solvent, and maybe I'll touch up around the sealed switch with a q-tip w/ vodka or whatever other relatively mild solvent I have handy. The Hoppes does wonders on copper
mods and removes oxidization almost immediately.
I usually take that opportunity to use some noalox or permatex on the contacts.