A small amount of Nickle based anti seize on the threads only (not on the seat). Perhaps almost as importantly to torque to the factory recommended value. Not too much. Not too little.
So that means Ford did not take into account anti-seize on the threads for the torque value, but dry threads instead. Its a low value so shouldn't matter much I guess, certainly does on higher torque values with dry, oiled and anti-seized threads. I usually only do the bottom half to 2/3 thirds because as you thread it in it travels up the plug threads if that makes sense.