Rolling a ball of clay is such a basic skill that it is one of the first things children learn when they play with clay at home. Rolling a ball of clay comes in handy when assembling other projects such as pinch pots. Rolling a sphere doesn't require a lot of dexterity, but making a nearly perfect sphere does take some time and effort.
Hold the lump of clay in your hand. Place your other hand on top of the lump of clay and squeeze the clay so the clay forms a rough ball.
Lay the lump of clay down on the table in front of you. Place your dominant hand on top of the lump of clay and roll it around and around on the table.
Pick up the lump of clay again. It should be moderately spherical at this point. Place your other hand on top of the clay and press the clay between your two hands. Squeeze the ball.
Lay the clay back down on the table and once again lay your hand on top of the sphere. Roll the sphere around on the table so that the ball becomes a near-perfect sphere.
Pick up the sphere and smooth any cracks or edges with your thumbs.