Directly from downward dog in the previous sequence of movements.
Vinyāsa 7: Inhale, Exhale, Inhale:
Inhale from downward dog as you slide your legs through and balance on your hands. Use the exhale to lower yourself down slowly between your arms. Bend your right leg until the sole of the foot rests as high up on the inner left thigh as possible. Let the right thigh relax. Grasp your right wrist with your left hand in front of your left foot. Lengthen the spine.
Note: It can be confusing to remember which hand grasps which wrist. To help you can use this memory hook: “The hand that wraps, grabs”.
For example, on the first side of Jānu Śīrṣāsana, you reach over the left leg. The left hand will grab the right wrist.
Vinyāsa 8: Exhale, 5 breaths:
Exhale and bend both elbows to the side and tilt the pelvis forward to come into the forward bend. Stay here until the fifth exhalation.
Note: Your right thigh is in extreme external rotation in this pose. When going into the forward bend, your pelvis will tilt forward. In this case, however, the right thigh should remain relaxed, to avoid turning inward with your knee bend at such an extreme angle. This could lead to undue pressure on the medial meniscus.
Vinyāsa9: Inhale, Exhale:
Inhale as you stretch both arms and straighten your back. Stay here for the exhale.
Vinyāsa 10 to 13:
Follow the flow of movements that you already know up to downward dog.
Vinyāsa 14 to 20:
Repeat the sequence of movements on the second side until you are again in downward dog.
In the traditional count, change here directly into the flow of movements of the next posture.
Effect: In yoga, hip openers are the combination of external rotation, abduction and bending at the hip joint. The strands of fibers at the hip joint socket wind in this direction. Jānu Śīrṣāsana is a pose that will develop precisely this 'opening' of the hip.