The first step to making your fish food isn’t anything to do with food. It’s getting an understanding of all the different diets throughout your tank. You cannot make the perfect meal for a fish that you don’t know. It’s important to try to mock the food they are used to eating. Unfamiliar food may result in starvation.
One way you can go about choosing ingredients is to look up the ingredients to the food specifically made for your fish then take the four or five most abundant ingredients.