Basically you want to cast the rod with a smooth sweeping action. Rotate your body backwards from the hips transfering weight to your back foot bringing the rod back to 2 o'clock. You are sort of bring your right hand in to above and slightly behind your right shoulder and your left hand is out in front of you. Now rotate forward transfering the weight back to the front foot your right arm is now extending and your left is pulling in toward you releasing the line with the rod now at 1-2 oclock. Do this in a fluid motion and you will have better, consistant casts and avoid tumbling. Avoid
snap casting as this will generally encourage tumbling.