When to use a block/nailer for ceiling drywall?

Wondering if there are any guidelines as to when you should provide a block/nailer for drywall on a ceiling. I ask because my ceiling is framed 24″ oc and it seems that one screw every 24″ around the perimeter might be too little. Is that assumption correct? Or, should I put a nailer in between the joists especially around the perimeter? None are there now. Thanks!