Regarding gaff placement, some say aim for the head, as most fish go where their noses point. For best results, wait until the angler has raised the tired king to the surface, lay the gaff across the fish's back and smoothly pull it home. Note the direction in which the king is circling and reach behind the line as the fish passes. This ensures that if the fish bolts, it doesn't break the line by dragging it against the gaff. Because kingfish events judge winners by weight, maintaining every ounce is crucial.
Low temperatures slow the loss of body fluids, and keep a heavy fish heavy.
The moment a king comes aboard, swing it into the box or bag, clip the line and close the lid, or zipper. You'll have plenty of time to remove hooks and leaders later, but the longer a fish flops on the deck or wiggles on the gaff, the more precious weight it loses. Naturally, a freshly caught king has plenty of juice and no lack of motivation for biting its captors. But even after the lights go out, there's still enough kinetic energy remaining in the muscles for a random flex that could inflict a nasty wound. Even stiff as a board, a king can hurt you if, when reaching close to remove a hook, your fingers graze those perpetually sharp teeth.