We recommend painting at least two coats. Very important when painting is to always allow a coat of paint to dry properly before the next coat of paint is applied. Depending on the colour being used a third coat would be necessary for example painting a white paint onto a darker surface.
The equipment you use for painting also plays a role. A foam roller leaves a much thinner coat of paint than a paint brush. Therefore, more coats of paint would be required when working with a foam roller.