Repairing cracks in your plasterboard/gyprock ceiling is not as easy as you would think. Most people think by just apply flushing compound to the crack, sanding it and then paint it fixes the problem. But more than likely if you do this the crack will re appear in just days.
Firstly you need to access the job and find out if there is an underlining issues which is causing the cracks to your plasterboard ceiling The processes in repairing your plasterboard ceilings may vary from paper taping your ceiling joints to back blocking between ceiling joists. If your plasterboard/gyprock ceiling cracks have re appeared over the year may you should think about a control joint.