Frequently a large smallmouth bass will strike your fly the second it lands on the river. In order to be able to set the hook quickly on these bass I like to have complete control of the shooting line as the fly line shoots out on the presentation cast.
In order to achieve this I form a O shape loop with my thumb and forefinger on my line hand and allow the fly line to glide through this as the fly sails out to the target. Then when the fly lands on the river I quickly close this loop in the fingers on my line hand. This enables me to have a tight line on the fly and I can instantly set the hook with both the rod and my line hand.