Lay your baby on their back on a firm, flat surface with plenty of clear space around them.
Shake a noisy toy to one side, roughly level with their shoulder, and let them turn their head towards it.
Move it slowly further round. The head leads, the shoulder follows, and the body often comes with it. If they get stuck halfway, a light hand on the hip is enough — never pull an arm.
Rolling starts with the head turning and the body following, so a sound that draws the gaze around is the natural trigger. It is the first time a baby changes their own position in the world, which makes it the beginning of independent movement.