First, understand the class and its strengths. They’re going to have great saving throws all around, due to Charisma being added. Their low stats are typically INT and DEX, but there are DEX build Paladins out there, so you’d want to have a general idea of whether that’s something that could be exploited against your particular Paladin. Their aura is their best support mechanic; pull their friends away from them.
Some ideas...