Yo,
Besides keeping in mind the comfort of your cheek weld, the important thing is to mount the scope as low as possible to keep the Line of Sight (the path of your vision) as close to the Line of Departure (the path of the bullet.) Normally, you only need to clear the objective of the scope. so if your scope has a 32 mm objective, you would use Low height rings. If your scope has a 40 mm objective, you would use medium height rings. This is just a general rule of thumb.
After choosing the lowest ring height you need to clear the objective and mounting the scope, then see if you'll need a cheek piece. If you have to mount high, it would be best to use a cheek piece, so that your eye is inline with the center of the axis of the scope. If your eye is off center, then you will induce more parallax error.
Hope this helps.
Bill