Fileting a fish is easy with a sharp knife. The cuts and presentation look so much better. The flexible blade makes fileting faster and efficient. Very little meat is lost when using a sharp knife.
Filleting is a skill learned through repletion and training. Watch a mentor or YouTube video to get an idea about what you need to do. Hands on instruction is the best way to learn.
A new knife will only stay sharp for so long. Scales, skin, bones, and fins will quickly dull the blade. The flexible blade is a great advantage when cutting but a disadvantage to sharpen. Most sharpeners end up smoothing the middle of the blade and not the edge. I know some fishermen that buy a new knife rather than sharpen the old ones.
There are lots of sharpening tools, gizmos, and gadgets available. The best edges that I have ever seen came from a medium grit oiled stone, finished with a steel or ceramic rod. The steels, ceramics, and other sharpeners are designed to bend the knife edge bur over. This can align the edge for a quick touch up. They are not the best choice for sharpening a dull blade.
The best edges that I have seen, used, and sharpened come from using sharpening stones. The medium grit stone, oiled with sharpening oil, is an awesome tool. You can get a Tri-stone variation, that gives you 3 different grits. Flex the filet blade as you push the point across the stone, away from you. Make 3 swipes, then do the other side. Use this repetition until you are satisfied. YouTube videos will help you understand what I am saying.
Once you have the blade the way you like it, take care not to ruin it. A filet knife is for slicing, not chopping and sawing. Use a separate knife for those tasks. Cartilage, bones, and scales will quickly ruin your edge. Tune up the knife using a small ceramic sharpener.
Another option is to use an electric knife. These work well for scaley fish like perch and panfish. Dedicated electric knives are made just for fish cleaning.
Whenever you are handling knives, think about safety. Kevlar gloves will protect your hands. Work the knives edge away from you. Use a sheath to protect yourself and the knife.
Cut it clean!