One important aspect of delivering the stone toward the broom is the placement of the gripper foot onto the hack. Always approach the hack from behind with your hips and shoulders square to the target. To that extent, make sure that your hack foot is pointed toward your target as you step into the hack.
As shown in the video, you want to place the ball of your foot about half way up the back of the hack. Place the gripper foot into the hack at the same level every time in order to reduce one more variable that could affect your curling delivery.