Using two flies is sometimes effective. By using a nymph with a soft hackle trailer or two nymphs is a good way to determine what part of a hatch the trout are targeting. The weighted nymph will help sink the soft hackle fly and put it in the feeding depth of the trout. When using two nymphs, you are determining which is more effective or just giving the trout a choice. My favorite way to rig is an improved clinch knot off the bend of the hook of the first fly with about 12 to 18 inches of tippet to the second fly.