Strike indicator set up for river nymphing. Leader with Small corky held in place with toothpick tied to a swivel eyelet. Yarn indicator can be used in place of a corky. (tie frayed Doubled yarn onto end of leader using a cinch knot) Yarn needs to be dressed to help its buoyancy. 

Dropper leader should be  equal to or less than the distance to the bottom.

Split shot can be added to dropper leader to get fly to sink faster.

Cast and mend immediately upon casting. Keep mending to maintain the dead drift. As the fly come past you mend and feed line into the drift to maintain the dead drift.

When the indicator stops, twitches or sinks .......SET THE HOOK. You will get the hang of it.

A two fly set up can be used for nymphing also (check regulations).  Replace the indicator with a big attractor dry fly and tie a nymph on a dropper leader attached to the hook bend or tie the dropper leader on a loop in the main leader.