Draw the hips back & raise them upwards so that the body forms an inverted 'v'. If you cannot get the heels on the floor with straight legs then either bend the knees or keep the heels off the floor.
Try to keep the neck & shoulders relaxed. Allow the weight of the head to lengthen the spine. Maintain the alignment of the head & spine. Don't allow the spine to sag or over arch.
Rotate the hips forward so as the to stretch the back of the legs without over arching the lower back.
Breath out as you relax into the pose.