You don't prep the grill for fish
The Result: Fillets that cling to the grill rack and break into little pieces when you try to flip them.
The Fix: Stickage prevention is a process, and it starts at the store. Skip delicate, flaky fish like tilapia, cod, or flounder, and go with firmer-fleshed fish, such as salmon, tuna, or swordfish. Pat the fillets dry with paper towels before grill time.
Now prep the grill. Set the rack over a hot fire for five minutes to burn away lingering debris, then scrub thoroughly with a grill brush. Carefully lift the rack and coat with cooking spray. Don't spray into the fire; if you can't remove the rack, swab it with oil using wadded paper towels held with tongs. But don't use the tongs for the fish: A spatula is less likely to tear the fillets. Let the fillets cook undisturbed for a few minutes. When they're ready to flip, they'll release cleanly.