Another thing that I just started this week and seems to work really well is rotating the diet that my fish have. I usually do a flake feed every other day. In the meantime, I was letting my fish snack on algae and snails/snail sprog.
In order to keep a varied diet for them all, I'm still doing flake foods every other day, but doing either bloodworms or baby brine shrimp in between. It seems to be working well, and my guppy fry are finally learning what feeding time is about. (All though for them it's more of a treat, since they are primarily eating algae yet.)