Depends on what you are intending to feed. If you are talking about crabs etc;
I got a few crabs, hermits, shrimps in my Peacock mantis' tank. I usually either crack open a few clams and leave them around the tank or crack open some snails and drop pieces where I know they live.
If the lights are off and you place the food around, hunger will do the rest.
If I keep my room lights on and the tank lights off its dim enough for the nocturnal feeders to come out. Its pretty cool to watch them feed.