The method is this: a single nymph (everywhere I've fished the method has been single fly only water). Often this is a size 16 or 18, with a tungsten bead, dressed slim so it sinks fast. The leader is long, long enough that you don't need flyline outside the rod tip. My set-up is fly, 5 metres of .10mm mono, 3-4 metres of .16, and then I have a 9ft tapered leader because this is the same rod that I use for dry fly fishing. If I need to cast further I lengthen the tippet.
So the idea is this: you see the fish (this is best), and standing slightly upstream of him, but downstream is fine too, you flick the fly accurately upstream. You can false cast the fly - yes I know - hell, you can even double haul it. As the fly sinks you keep low and watch the leader like a hawk. Keeping your arm fairly straight gives you control over the loop of mono that curves to the water. You are trying to stay in touch, no drag, and you are using the leader itself or where it enters the water, to determine a take. This gives unparalleled take indication, because the sensitivity is unbelievable and you can in touch with your fly - there is no slack line. Keeping low allows you to see the leader. You follow the swing of the leader with the rod tip, and lift it at the end of the swing.
Now you can either attempt to lift at the end of the swing, immediately in front of the fish, or twitch the fly just as it passes by. If you can see the fish, strike on any deviation. If you can't see the fish strike on any hesitation of the leader. You will be amazed at him many fish you strike from the smallest of deviations, fish that you would never catch otherwise. You will need to work on your line management skills because you don't want 5 or 6 metres of mono tangling around your feet!
This method has revolutionised my nymphing. I don't claim to be great at it, but I do know I now catch a hell of a lot more fish on technical waters than I ever did before. And it's great fun too!