To train your arms to work in sync with your body turn, all you need is a club and a towel, as Titleist Staff Instructor Trillium Rose demonstrates in this video.
Arm Connection Drill
1. Take a rolled up towel (or a head cover or even a folded up golf glove) and place it under your lead arm. Gently squeeze your lead arm against the side of your chest to hold the towel in place.
2. Take your golf stance, wedge in hand, and lean into your lead foot.
3. Turn back so that the lead arm glides across your chest, still securing the towel. Start with little half-swings, half speed.
4. Rotate your upper body toward the target as you let the wedge fall and brush the ground. The arms simply go along for the ride. Keep your lead arm connected and the towel in place while focusing on rotation.