Sit upright on a firm surface with your feet hip width apart.
Move forwards, so that you are sitting close to the edge.
Tuck your feet back so that they are under your knees.
Place your arms on the sitting surface either side of you, wider than shoulder width.
Lean your weight forward and use your arms and legs to lift your bottom from the surface.
Use your hips to move your bottom to one side before siting back down.
Continue these movements to move your bottom in one direction.
Practice the movement in the other direction.