To double or even triple your chances of finding the right nymph the trout are eating, or give the trout more options is to use a tandem rig.  A tandem rig is when one nymph is tied on the end of your leader or tippet then another nymph is dropped off your main nymph about a foot and a half to 2 ft.

When fishing a tandem rig, I usually like to fish my bigger nymph as my first nymph then drop my smaller nymph off that.  If I'm fishing two nymphs the same size, then i usually make the second nymph the one i have more faith in or the one that rides a littler higher in the water column.

My rig usually goes something like this (this time of year when the water is low and clear otherwise, my tippets probably 5x all the way)-

3ft piece of 5x tippet off my leader, 2ft piece of 6x tippet off that, then my first nymph is usually a size 12-14 beadhead prince, bh hares ear or bh stonefly with 2 small black wingless split shots a few inches above, with another 18-24" piece of tippet. I tie that through the same hook eye as the first nymph (some tie directly on the hook) then another small split in the middle of this piece of tippet. Then I tie on my 2nd nymph usually being a size 16-20 prince, caddis larvae, or pheasant tail.

Once you've mastered the double nymph rig with a lot less tangles, try 3 by doing the same thing you did with your first dropper off of your second nymph.  With the 3rd though, I would leave out the small split halfway on the piece of tippet and maybe go with a soft hackle fly or something that will can cover 3 different fieeding lanes of the water column.

This should greatly improve your nymphing success since trout can be so picky as to where in the water column they are feeding and what nymphs or flys they are feeding on.