The game itself will tell you in a loading screen that Ice type enemies are weak to Fire. General consensus seems to be that hitting an Ice elemental enemy (e.g. Ice Keese) with a Fire element weapon will do around 10 times the normal damage. This also seems to work the other way around, hitting a Fire element enemy with an Icy weapon will do 10 times damage.
However, the one I'm not sure on is Electric element enemies. Are they weak to electric themselves? Or do they simply take regular damage from everything?