This is actually a complex pose, where so much is happening in the body at the same time. Tight hamstrings and shoulders will affect the position, so we need to work on that. Once you get use to downward-facing-dog, it will have an amazing affect, long-term.
Strengthen areas: Shoulders, arms, wrists.
Stretch areas: The spine, shoulders, hamstrings, calves, wrists.
PS! You need a strap / band / scarf for this session.
Focus on the breathing is key in all exercises.