First, you need to learn the techniques for controlling knife, only then you can make proper fish fillets. Tips for filleting a fish differ slightly based on the size and type of fish. Say for example, the head part is separated first prior to cutting a small fish. While in case of a large fish, it's not necessary to remove the fish head.
The first thing that you should know about making fish fillets is choosing fresh fish. Ensure that it has bright eyes and does not stink. If possible, lift the gills to check the color within; a bright pinkish red indicates fresh fish, while bluish coloration is a sign of rotten fish.
The type of knife that you use also matters a lot in filleting a fish perfectly. That is the main reason why, some professionals prefer using custom knives, while others can make fillets with normal kitchen knife. The trick is to use a sharp knife that cuts fish flesh smoothly. Based on your preference, choose a good quality knife that you find comfortable in making sharp cuts. Also, get a clean and large cutting board.
Coming back to learning how to fillet a fish, there are two common methods. The first is to start from the head, and the second is filleting from the tail portion. Here, we shall focus on the first technique. Hoping that you have already cleaned the fish (remove gut), place it over a flat cutting board. Place the fish in a comfortable position for safe cutting, or you can place with head pointing towards you.
Locate the fins just below the head, and make the first straight cut below the pectoral fins, in the soft tissue. Make this cut straight and perpendicular to the backbone. Stop as soon as you can feel the backbone (do not cut through bone). Hold the fish head and belly flap with right hand, and open the cleft slightly. Tightly hold the knife with your left hand and be ready to make horizontal cut.
As you flip the knife to 90 degrees, its blade will remain adjacent to the backbone, but parallel to it. Pointing the cutting edge towards the tail direction, make the horizontal cut. You can use the backbone as a direction guide. Slightly lift up the belly flap with right hand and continue cutting the rib bones, moving the blade towards the tail. Watch the knife as it comes closer to the dorsal fin and anal fin. Finish off the second cut by running the blade just above the anal fin to collect maximum meat.
With this step, you are done with making the first fillet. Moving to the remaining side, flip your fish and hold the fish head with your right hand. Again make a straight cut, just behind the pectoral fins and at right angle to the backbone. Make the horizontal cut as mentioned above along the backbone. Once you get the second fillet, you can start cleaning the two fillets, and removing the ribs to get boneless fillets.
Have some patience while learning to do it. It will be just a matter of few trials, and you will become a master in filleting a fish. The result will be thick boneless fillets, which you can use in any fish recipes, that you can think of. Whether you grill, make stew, or simply fry them, fish fillets taste delicious.