I'm no pro betta person but feed them a variety of foods, make sure there is no sharp objects in the aquarium (such as hardscape). Give them plants that they can rest on and make sure that tank mates are compatible with bettas (I don't think you will be adding many tank mates in a 5 gallon though), make sure flow is low, and I would give them areas of shade (floating plants or large leaf plants). I would feed a small amount in the morning and a small amount at night if possible. To reduce stress at plenty of hiding places.
I know these are basic tips but they are very important in my experience!
Have fun!