I've owned different kinds of fish, but never any betas. I googled Beta Fish and came up with a website that had this:
Recommended Diet. Floating Food and Freeze Dried Blood Worms both available in most places that pet fish are sold. Bettas are not an active fish, so they don't require as much oxygen or as much food as energetic active fish do.
Feed your Betta twice each day. I feed my Bettas in the morning and in the evening.
Be careful not to feed your Bettas more than they will eat. Remove uneaten food with a small net after 10 minutes. Click here for more about feeding fish.
I feed all my Bettas a few Black Worms every other day. Click here for more about Black Worms.
Here's the website itself so that you can do the 'click here' thingys if you want: http://www.aquariumfish.net/catalog_..._more.htm#diet
Hope that helps - and Good luck with your new addition!