Fish are far better being underfed than over fed. How much you feed is going to vary a lot depending on how good your filtration is!
If I dont know much about peoples stocking, my advise at work is to feed once a day and "assume your fish's stomach is about the size of one of its eyes". This is talking about tetras etc... it at least makes people think more about just how much food they are chucking into their tank.
The more you can feed without causing problems, the better really but more feeding = more cleaning + more water changes.
I always fed my fish once a day, i would create my own mix of flake and micro pellets and give a small feed and let all the fish fill themselves up. Then I would do a frozen food feed (10-15 minutes later) and then when that was all cleaned up, i would chuck in the algae wafers or novotabs for cories etc.
If at any point they dont eat all the food, they dont get the next stage/s of food. Anything that got left over (very rarely!) i netted out... and i did 50% waterchanges with gravel cleans every week.