If the bottle of polish is brand new, we do not recommend shaking it because in most of the cases, shaking the bottle can create air bubbles that will rise up to the surface.
Instead, simply roll the bottle upside down between your hands.
When a bottle of color has been unused for a long time, we do recommend you to shake it a little bit before you start your nail prep, so the liquid has time to settle and the bubbles to disappear.