To begin our exploration of the body, I invite you to consider the reptile. Our reptile minds sit at the very roots of our brain, running our bodies and keeping us alive.
Without the emotional mammal and thinking monkey brains that evolved later, the reptile has no suffering/stress and no distractions. They are naturally calm and focused. This is best starting state for anything you need to do.
You have this mind with all of its innate qualities deep within you, working away constantly and tirelessly. In other words, you don't have to try and develop this aspect of yourself – the deep calm focus. Rather, you simply need to get in touch with what's already there.
When you observe a breath or body sensation, you are making a connection between your human observer mind and reptile body mind. In so doing, you will tap into and express some of your ancient and innate reptilian calm-focus. Notice this effect and use it to your advantage!