On our technical South Island lowland rivers you want a little play in your leader to deal with those tricky micro currents on your subtle film flies.
Piles, serpentines and other presentations become essential on these waters but another great tip is to design your leader to generate slack right down at the fly.
Take a 10' (or 14' ) trout hunter leader and attach 4 - 5' or more of soft, good quality co polymer and let it fly. The longer, lighter tippet till dissipate energy from the tapered leader and allow not only the fly to present well on the drop, but back it up with the extra slack required to enable a drag free drift.
A good quality, soft co polymer suits cdc and other film flies without sinking them and creating disturbance upon pick up, and a supple fluorocarbon provides extra abrasion resistance for blowflies etc close to the willows and in rocky riffles.