Don’t harden your upper body at any time. Stay calm and keep your body relaxed. When you tense up your body, you make pivoting, turning and overall movement harder. Thus, keep your shoulders loose and hands-free.
Do not tense or contract your muscles, just enjoy the smooth and fluid movement. If you’re just starting out, this might take time, but it will eventually happen. Also, don’t relax your arms completely, allow them to sway a bit as if you were on a walk.