The Single Leg Dead Lift starts with a stance that is narrower than for the Barbell Dead Lift. Maintain a neutral spine by bracing your butt and abs then pull your hips back. Hinge through your hips to bring you down to the kettle bell. You should find yourself with your shoulders over the bar and hips at a height between your shoulders and knees. Firmly grab the kettle bell. Begin to lift the kettle bell by driving your heel into the ground and standing up to a natural position. Be sure to pull the kettle bell in tight to your body while standing keeping the bar against your legs.
Lower the kettle bell by leaning forward and pulling your hips back, maintaing neutral spine and keeping the kettle bell close is essential. Ideally you will finish lowering the kettle bell in exactly the position you began in. If not stand up and reset.
If you notice your knees keep shooting forward or in before the kettle bell has passed them then you are not pulling your hips back or leaning forward.