Sit on a chair and extend one of your legs forward.
Keep your other leg's knee in line with your toes.
Depress your shoulder blades and keep your chest open.

1. Engage your glutes and hamstrings. Slowly stand up with one leg. Your body (pelvis) should move forward over your toes. Keep your torso at the same angle.
2. Slowly sit down without letting your shin move back. Touch softly the chair.

A tip to engage your posterior chain: try to pull back your heels against the friction of the floor (without real movement)