Make sure you put a wet cloth underneath your chopping board, so that it doesn’t slip. Lay the fish on the board, and make a diagonal cut behind the fins behind the gills. Turn the knife, so that it presses flat against the spine. Put your hand firmly on top of the fish and run the knife along the spine, till the fillet comes of. Flip the fish over, and repeat the process.
Cut the stomach and ribcage of at an angle, so that you keep as much meat as possible. And finally, remove the bones with a pair of fish-pliers.
If you serve the fish in individual portions, it good to make little cuts in the skin. That technique has a few benefits. The skin won’t curl up and will go crisp al lot easier. You can stuff the cuts with herbs, and the flesh will take on any flavourings a lot better.