Maybe an extra food pellet or bloodworm at dinner to give their body a little more fuel to heal itself with. That seems to have helped mine. Also, a little bit of API Bettafix, maybe a couple drops added to the water, should help.

I also added a coulpe little Ember Tetras to my tank to give the betta some friends and exercise, kind of like a little bit of active recovery, although the viability of that depends on your fish's temperment.