If the design of the ceiling is finished, such as whitewashing or painting, then for this it is simply necessary to eliminate cracks and bumps.
The most noticeable defects appear to dry out the first layer of paint. Therefore, they must first be eliminated, and then you can cover the surface with the second, third layer of paint. The surface defects in daylight are better visible. The ceiling should be examined so that none of them are unnoticed.