Correct posture is incredibly important for the successful practice of breath control. It enables efficient breathing as well as stability of the body during practice.
The spine should be kept tall and erect so that the chest does not collapse forward and compress the lungs. If you find that your knees are elevated above your hips, it can be helpful to sit up on a cushion or blanket to raise your hips and lengthen your lower back.
Roll your shoulders up and back, creating space across your chest.
Tuck your chin in slightly to lengthen your neck, imagining that the crown of your head is being drawn up towards the ceiling.
If comfortable, allow the eyes to close or direct them slightly downward to the space just in front of you.