Complete all eight AR Training exercises to unlock the achievement. The first four unlock on your way to the Steel Mill for the first time, and completing them unlocks the grapnel boost upgrade which allows you to glide indefinitely by grappling from building to building without ever touching the ground. The trick to the advanced exercises is to time your dives properly. Stopping the dive early by letting go of the trigger and barely pulling back helps make it through the tight corridors. The video below contains all the exercises.