It depends greatly depending on which corals. The size consideration is really the difference for different corals. Certain corals are meant for filter feeding tiny particles and others eat bigger chunks of food. The common element is that they all eat meaty fare.
They all also need to have proper levels of calcium, magnesium, trace elements, and iodine, for optimal health.
Brain corals will benefit from Cyclopeeze like Heath said and Mysis shrimp, all soaked in a vitamin supplement like selcon before feeding.