This could lead to some long posts.
There is so much information, techniques and oppinions to fill a library.
Basically...fish where your nymphs bounce along the bottom and your indicator is at the surface. This takes constant adjustments (many more than the average angler is willing to make). Add and take away shot as needed and move the indicator along the leader (height of the water in slower pools; and 1.5 water depth in the faster areas).
Stringing nymphs together is productive, but may be hard to handle for a beginner.
Drag, or pull on the fly line/leader from the water has to be minimized or the fish will know something isn't right. This is usally accomplished by keeping as much line off teh water as possible or through mending. (I prefer keeping the line off the water because it also leads to quicker hook setting abilities)
Biggest thing is practice. If your aren't catching fish your doing something wrong. Try faster riffles and runs and stay away from deep pools, of course this is my oppinion.
Side note, stocked fish, especially those who have grown whery of anglers, are difficult to catch and are unpredictable in feeding patterns. Try just above and below stocked locations or wild trout streams. These fish will behave more like...well fish.