Ceilings and wall cracks are very common and can be easily repaired. Walls and ceilings are always expanding and contracting aren't nearly as stable as most perceive them to be. Any cracked ceiling repairs must have have the flexibility to go with the natural flow of a structure in order to hold its good looks.
Start by sanding the area surrounding the ceiling crack, and then apply fiberglass spackle tape along the entire crack. Next, apply spackle over the tape in three thin coats, using progressively wider spackle knives, ranging from three inches up to ten inches wide, until you have a seamless surface. After the area has dried, sand the ceiling well and apply a coat of primer, followed by paint specially formulated for ceiling applications to completely hide your cracked ceiling.