My favorite fly for carp is a #8 bead head prince nymph. The key is to find them feeding in the shallows with their tails down and their heads up or locating mud puffs in the flats. If you can find them doing that, it's magic although they spook so easily. Sometimes I'll throw to over 20 feeders before I manage the perfect presentation and get a take. More times than not, they spook because the fly line hit their back or the fly can down too hard too close to their head, or they saw me before I saw them. And their pickiness for a particular fly pattern can put a trout to shame.