Pull the sit bones back. This will bring the weight forward slightly.
Roll the thighs inwards.
Lift the chest and use the back to broaden it.
Heels of the hands push down as the shoulders roll back to help open the chest.
Chin drops forward (Jalandhara bandha).
Lift and lengthen the torso to engage Uddiyana bandha.
Drishti is Nasagrai to the nose.
Stay focussed on the length of the spine and Uddiyana bandha. Keep the breath steady. It is a great indicator of your practice. If the breath is harsh, fast or you find yourself holding it, relax. We must lose our western approach of wanting and of aggressive behaviour. You have the rest of your life to work towards the posture.
Build up to 25 breaths.
Relax and smile
Modifications
If the hamstrings are tight, lean back slightly to help release them,
or bend the knees and keep the spine long.