If you are using sinking pellet food.......feed 3 pellets twice a day or 4 pellets once a day. That seems to work well with my betta. Their stomachs are pretty small and they don't need much. Fast him for one day once a week.
Floating will work too. Their mouths are actually built to eat from the surface. I was just thinking about my pellets. I use Omega One betta pellets. They float for a bit then sink.