When placing the ball on the a tee, it is important to do so such that the ball will be struck properly by the driver. As such establishing the correct height is extremely important.
The correct height is completely dependent on the height of the driver being used. The top of the driver face should be at the same height as a point on the ball approximately 2/3 of the ball's height. This allows the sweet spot of the driver to connect with the center of the ball while keeping the bottom of the driver off of the ground and thus maintaining top swing speed through the shot and most importantly at the moment of impact.