I am writing a tip for ball games.
When you play any of ball games, Baseball, Golf, or Tennis, it is generally important to turn your waist first before start swinging your arm. Tuning the waist initiates smooth and sound movement of the body to hit a ball on the axis of rotation.
The phrase "Turn your waist first" sounds OK? How “rotating your waist”, or “moving from your waist” sound like?
I think I'd say 'turn from the waist' or 'turn at the waist'. (After a Tai Chi class I might say 'lead with the tan-tien')