How I do it is.
Heavier fly on top attached to the tippet, then add 12-18" of tippet (tied with an improved cinch knot off the bend of the hook) the add the second fly, 8-12" tippet (again off the bend) then add third fly.
Try to open your loop a bit on your cast seems to help me avoid tangles.
I normally use 3 flies till I get an idea of what they are snapping at the switch to 2 flies,
EG. i start with a BAW, copper john, pheasant tail. if i find all my hit are on the john I'll switch to 2 johns of different colour. or the worm and john.
lost a double this year on a red and green john rig. (one day fishies.... oh yes one day)