I wish I caught more Delaware fish with flies, but get plenty with lures and bait. Basically it all takes time.
First step: explore, explore, explore until you know the stretch like the back of your hand. Know the deep slots where the fish spend the day. In the deep slot look for points, drop-offs, etc that hold fish. Knowing the general shape of the slots is not enough - it helps to now all the little features where fish hold. Most of these features will be submerged and subtle. During the day I like to fish nymph/crayfish sort of stuff in brown/orange/black colors slow drifted near the bottom. A master jig tier once said every color jig works as long as it is black or brown. Keep it simple. Smallies like a little orange in the mix.
As you are wading around in the shallows take note of where you see the most minnows and bait fish. Come back at night and fish some kind of minnow fly. I like pencil poppers and Gartside Gurglers for the surface hit. Look for swirls and fish breaking. My best fly fishing is at night/in evening when I see fish busting into schools of bait. Those fish are on the feedbag and hit well.
Fish a lot and watch what others are doing. How fast is the water where the fish are hitting? Do the heads or tails of pools seem better? Get to know the pattern the fish use - and keep fishing through the year because it will change.
I like white flies for minnows, but a chartreuse/white Clouser minnow is rarely a bad choice. At night white or black can work.
The only secret I know is to work hard and keep changing your tactics until you find something that works.