It is most important for you to always practice with the same chair and footstool height and to place the footstool approx. 6" (15cm) away from the left leg of the chair. Always sit on the front edge to avoid knocking the lower bout of the guitar against the chair (see photo A). The chair and footstool height should enable your left thigh to slope down at a slight angle towards the body (see photo A). The left leg should be at right angles to the floor (see photo B) and should not be allowed to be pushed away by the guitar.
Viewed from the side (see photo A) the back should be straight, head relaxed and not leaning forward over the guitar. Viewed from the front (see photo B), the body should be straight and upright, the guitar resting at approx. 40 degree to the floor so that the head of the guitar is just below eye level but not too horizontal.
If you follow the rules outlined above, the guitar will be supported in four positions:
The correct sitting position will provide a fixed position for the guitar and allow complete freedom of movement for the left arm.
Viewed from above (see diag.) the guitar must be placed at a right angle to the left leg. Your upper body should be turned slightly to the left from the waist, to enable the upper bout of the guitar to rest against the right side only of your chest, and not flat against it.
This is vitally important as only this position will allow total freedom of movement for the left arm and hand.