Mozzarella sticks are a bar food institution because they deliver an experience almost impossible to replicate at home: the dramatic pull of molten mozzarella from a perfectly fried, seasoned crust. The pull is the whole event.
The critical variable is temperature. The mozzarella must be frozen before breading, and the oil must be hot enough that the crust sets before the cheese melts through. Marinara for dipping. Served immediately. If they sit more than two minutes, they have peaked.