Learning how to fillet a fish can take some practice but has rewarding results.
The first time you attempt a fillet don't expect it to be perfect or it to be a fast process, some will be lucky to have more meat on the fillet than what is left on the skeleton of the fish.
That being said, you first want to start with a good, sharp fillet knife, you can get a good quality knife under $20, I wouldn't waste my time with a really cheap fillet knife, I would stick within the $10-$20 range.
Attempting this with a dull fillet knife will frustrate even the most experienced.
You need to decide how you are going to be cooking the fish? A filleted fish can be cut into chunks, grilled, baked or fried. In most cases you will want to remove the skin and scales.
If you have a redfish and plan on grilling it leaving the skin and scales on the fillet is a great way to grill redfish. But don't try to do the same with snook because the skin and scales will give it a somewhat soapy taste so the skin will need to be removed.
Now that you have decided how you want to cook your fish and you have a sharp fillet knife, make a cut right behind the head of the fish.
Next, insert your knife at the top of the cut you just made and start making your way down the backbone of the fish. Just try to get the fillet started by inserting your knife about a 1/2 inch to 1 inch deep for now and go all the way to the tail.
Once you get the first pass made, lift the edge of the fillet and work your knife deeper into the body of the fish keeping your knife against the backbone.
On smaller fish the easiest thing to do is cut through the ribcage and remove the rib bones when removing the skin.
On larger fish cutting through the rib bones will be difficult so you can cut around the ribs while cutting your fillet if needed.
Hopefully you have your fillet by now, to remove the bones from the ribs (if you cut through them) use your fingers to feel where they are located and cut around them. Turn the fish over and repeat the process on the other side.
Once you learn how to fillet a fish, you will be able to have your own fish that looks like it came from the supermarket.