you need good breath support for the calling. Supposedly your supposed to tongue each quack like saying "ten" but i grew up playing instruments and find it sounds better to just use good breath support without tonging and using your lungs. As far as the feeding goes, i double tongue in series of two saying: "ti-ca, ti,ca". look up how to double tongue a saxaphone on youtube or something and that's the best way to do it. You don't need to do it (feeding call) fast like competition calling, ducks never really go that fast. I always stick to between 4 and 7 quacks at the most. Do like a faster greeting call when they're a ways away coming towards you. If they keep coming, dont call and just do the feeding call a little. If they cirlce, let them do one full circle and when their butts are facing you blow 5 excited quacks with the first one held out longer. as they circle more keep doing the feeding call. As they do a second circle, make the calls even more excited and faster calling to their butts again. If they're on the water a little ways outside your set try mixing a single "quack" with the feeding call.