Identify the cause of the crack
Check for water leaks, roof damage, or structural movement
Remove loose paint, plaster, or drywall around the crack
Widen the crack slightly with a utility knife if needed
Clean out dust and debris
Apply joint compound, spackle, or plaster patch
Embed mesh tape for longer or recurring cracks
Smooth the repair with a putty knife
Let the patch dry completely
Sand the area until smooth
Apply a second coat if needed
Prime the repaired area
Paint to match the ceiling
Repair any source of moisture before patching
Call a professional if the crack is large, growing, or accompanied by sagging