The simplest set of instructions I've seen (on lag, the wrists, the hips and the arms) has come from a long time Pro/Instructor named Gregg McHatton.
Two years ago I was frequently shooting over 100. Switching between concepts of instruction (that almost always contradicted each other) and changing equipment as frequently as changing socks...
Stumbled onto some vid's of Gregg (YouTube) a while back; they changed my game. Still like to buy/view a DVD or two (it's a sickness!). Read a lot of different stuff written by a lot of folks that purport to be expert; but nothing has helped me more than McHatton's simple concepts.
hip turn is the engine
swing low and left (for righties)
I never had "Lag" until I softened the wrists... I'm down to a 13 (Hand. Index)...