I fed three times a day at first until i got him eating more and more. Months later I am still feeding the tank twice a day. I also have a mandarin in there too so it works out for both fish.
I use a turkey baster to shoot the food to him, I have him trained to go to the right corner of the tank when it's feeding time. makes life easier if he associates a place for food. Also, I turn off the flow in the tank for maybe 10 minutes when I feed, the dragonets are not the most efficient eaters so they need some extra time to find and consume the food, especially if you have other fish like clowns that gobble the food up so quick.