Feel for any remaining bones first. If necessary use pliers to remove them. I find needlenose are best.
To start, hold the narrow end facing you. Place a sharp knife between the skin and the filet at a 45 degree angle. Cutting against the skin, hold the knife steady to avoid cutting the skin and cut downwards using a very slight sawing motion. After you get about an inch down the skin it should be easier to get a firmer grip. Use paper towel if you need to.
Make sure you use a long, flexible and sharp knife.