Squat with your feet as close together as possible. (Keep your heels on the floor if you can; otherwise, support them on a folded mat.)
Separate your thighs slightly wider than your torso. Exhaling, lean your torso forward and fit it snugly between your thighs.
Press your elbows against your inner knees, bringing your palms to together in Anjali Mudra (Salutation Seal), and resist the knees into the elbows. This will help lengthen your front torso.
To go further, press your inner thighs against the sides of your torso. Reach your arms forward, then swing them out to the sides and notch your shins into your armpits. Press your finger tips to the floor, or reach around the outside of your ankles and clasp your back heels.
Hold the position for 30 seconds to 1 minute, then inhale, straighten the knees, and stand into Uttanasana.