I personally don't kill fish very often as well, as i'm largely a catch and release angler. But occasionally if i catch a nice flatty or whiting I will taking it home. I find the best way to kill them is to use the old whacking stick method. A precise blow to the head with a blunt object will quickly kill any species. Aim just behind their eyes, I find this knocks them out quickly. I also like to fillet the fish straight away too, then put them on ice. If your gunna go to all the trouble of catching a fish for the table you may as well keep it as fresh as posible.