Small meals more frequently are better for digestion than one big meal once a day.
Most breeders will say small amounts three to four times a day
Most pet keepers feed twice
The missinformed will feed once a day
The instructions in the "bettas in a vase" are dead wrong
If you're feeding pellets, it's pretty easy. If you are using a filtered tank, still the water (turn filter off), and drop in each pellet one at a time. Make sure the betta -eats- the first pellet in the tank before you drop in the second. It make take some time for him to get the idea, so you may want to use a feeding time cue, such as tapping the side of the tank gently to let him know chow is on the way (operant conditioning). But making sure the betta actually ingests every pellet that falls into the tank will keep your tank 100% cleaner than simply rubbing six or seven pellets off your fingertip into the water. Sure it takes longer, but your betta will be healthier for it.
Usually 2 to 3 pellets three times a day is best. Most people do about 4 to 5 pellets twice a day, which is fine too. Don't feed your betta until he looks fat a bloated. This can cause the pellets to swell with so much water that they damage his internal organs or give him swim badder disorders. Your betta may learn to "beg" when you approach his tank, don't be fooled, if he's being fed properly, he's not hungry, he's just doing his Palvo's dog impression for ya.
If you're using an unfiltered tank, change the water -after- you feed so you can take out any icky stuff the fish didn't eat before it rots in the bottom of the bowl.
~~Colesea