Keep the chin tucked in
Keep the shoulders relaxed, down and back
Sit with a curve in your low back (see picture) as this allows the pelvis to sit directly under the points of your shoulders so you sit on the bony points of your bottom.
Sit with your hips, knees and ankles at right angles, thighs level with knees.
Keep the head in midline, on top of and in line with the shoulders
Sit with your weight equal on both sides/cheeks of your bottom, well back in seat and feet flat on floor.