I have found - working with my teenage daughter - that starting with the opening drills in ETK and the warm up for S&S have been a great intro. in particular:
wall facing squats, goblet squats, halos, wall facing kb deadlifts, and pelvic thrusts before any swings are worked in. my daughter had issues with the swings until she could recognize the proper position of the lower leg, how to bump the tush out and back, when to properly bend the knees, how to tighten the glutes and not bend the upper body back, how to focus on the abbies and glutes into the plank position. these introductory exercises helped to guide her body into the swing.
then, of course, TGUs - as per Dan John's suggestion - with a cup of water on the fist - and then moving to small bells until the motion is technically sound.
Do these for a couple of months and then S&S will do the trick going forward.