It depends alot on the species being kept. Certain fishes, like the anthias, need more regular feedings to stay healthy. Daily is a good place to start, but in our captive/mostly stress-free aquaria, overfeeding should be avoided. Keep an eye on the fish themselves... tangs and other herbivores need fed more often as they have very short digestive tracts and process food much faster (and much less thoroughly!).
I typically feed my fish 4-6 times per week and also throw in nori for the tang and rabbitfish irregularly to keep them fed.
What I mean by watching the fish is you should keep an eye on their bellies and just behind the eyes. Those areas should stay fairly well fat. If you see pinching, they need more food. Also, if you see any odd diseases or lateral line erosion, you likely need to feed more/better foods.
Wade