Aim where the neck meets the head, not at the body and not at the beard. A turkey's vitals for shotgun purposes are the brain and the upper spine; body hits with shot cripple birds that are never recovered.
Wait for the head up and still. A strutting gobbler has his head tucked into his fan — cluck once and he will periscope up, which is the shot. If he is walking, let him take one more step and stop.
Keep your cheek welded to the stock. The overwhelmingly common miss on turkeys is shooting over the bird because the shooter lifted his head to look, which is exactly what happens with a rifle.
After the shot, get on the bird immediately. A pellet-stunned turkey can recover and fly, and putting a boot on the head and neck ends the hunt cleanly.