I usually feed mine 2-3 SMALL meals a day (depends on the fish though). Morning, night and sometimes lunchtime. I also fast some fish depending on species once a week for a day or so. I usually feed a different food each meal so they might get flakes in the morning and night with bloodworms, microworms, peas, etc at lunch. I also put blackworms in the tanks once a fortnight for my eels and catfish to forage for, the other fish also eat these when they are added until the worms burrow into the sand.
Generally though, fish with shorter digestive tracts, such as guppies and fry, and fish not normally known for going long periods of time without a meal in the wild will be fed smaller portions more frequently and not be fasted. Fish who are known to go quite substantial times without eating in the wild, or whose digestive tracts are alot more adept at absorbing nutrients will be fed less frequently and sometimes fasted. It really is species dependant though and I like to keep their food intake as close to their wild counterparts as I can, within time constraints, etc.