What are the common causes of cracks in plaster ceilings and how can they be effectively repaired?

Common causes of cracks in plaster ceilings include structural movement, moisture damage, and age-related deterioration. To effectively repair these cracks, start by cleaning the area, applying a plaster patching compound, and smoothing it out. For larger cracks, use mesh tape before applying the compound. Sand the area once the compound is dry, then prime and paint to finish the repair.