This food reference provides all the information you need to make good food choices for your fish.
Do not overfeed your fish. Different fish are built to eat different types of foods. Do some research on your fish and determine what dietary type your fish is - Whether herbivorous or carnivorous or omnivorous.
Find out when and where the fish prefers to eat whether from top of the water layer or immersed in water. You need to experiment on this.You need to provide a balanced nutrition for your fish.
Always provide fresh food for your fish. Some fish eat only vegetarian foods. For them you can provide flakes of algae ,pellets and vegetable sticks.