I tend to keep to a rule of three. He gets three things per day, whether it be pellets, flakes, brine shrimp, or bloodworms. So some days, he'll get two pellets and a flake. Some days, he'll get a flake, a pellet, and a bloodworm.. etc. I try to switch it up every day and work with different combinations. I don't fast him, but on weekends, he gets two things per day rather than three.
Every betta's different. Try to keep some variety and make sure you're using high quality food. Read the ingredients. The first ingredient should be some form of protein. It's better if it lists the specific source (Herring, shrimp, etc) rather than just "fish meal".