Air time
A fish out of water is a fish suffocating. Under thirty seconds is a target, ten is better. Have the camera ready before the fish leaves the water.
Support
Hold horizontally with a hand under the belly. Hanging a heavy fish vertically by the jaw damages its spine and organs.
Hooks and gear
Barbless or pinched barbs come out fast. Circle hooks on live bait set in the jaw hinge rather than the gut. Land the fish quickly; a fish played to exhaustion often swims away and dies anyway.
Warm water
Above roughly 75 degrees, mortality climbs sharply. If you cannot revive a fish until it swims off under its own power, keep it or stop fishing.