What are the common causes of a crack in ceiling drywall and how can it be repaired effectively?

Common causes of cracks in ceiling drywall include settling of the house, temperature changes, or moisture issues. To repair effectively, first, clean the area and remove any loose debris. Apply a mesh tape over the crack and cover it with joint compound. Smooth the surface with a putty knife and let it dry. Sand the area, apply a second coat of joint compound if needed, and finish with paint to match the ceiling.