Sit down on a mat with your trunk upright, leaning back slightly with your legs at the width of your shoulders. Bend your legs to about a 90˚ angle between your thighs and calves at your knee joints. Grab the weight and hold it at its ends in front of you at chest level. Keep your shoulders in a neutral position.
From the starting position rotate your trunk and while moving the weight from side to side. Keep your bodycore firm and do not overly bend your spine. Inhale in the starting position, fix the trunk with your breath in and exhale while returning to the starting position. Exhale while alternating to the other side and inhale going back to the starting position.
Pay attention to your body posture, keeping your body core firm, pelvis in a neutral position and not overly bending your spine.
Keep your knees in the direction of your toes and at shoulders width all the time.
Keep your shoulders in a neutral position and do not bend them forward.
Exercise in front of a mirror to watch and improve your technique.