To repair cracks in a drywall, cut out an outline to the depth of the crack on both sides of the crack, fill the crack with an all-purpose joint compound, and allow the compound to dry. Sand and paint the surface to complete this process.
Using a pencil, draw a line on both sides of the crack so each line is about 1/8 from the crack, and cut along each line with a utility knife so the depth of the cut matches the depth of the crack. Clean the crack by scraping it with a screwdriver. Push each side of the drywall, and mark where the wall moves. Using a hammer, drive enough drywall nails into the marked spots.
Combine all-purpose compound with water, and mix it to the consistency of a toothpaste. Use a putty knife to spread about a 1/8-inch layer of the mixed compound over the crack, filling the entire crack with the compound and spreading the compound about 6 inches along the crack. Tape the entire crack so the central crease of the tape faces and aligns with the crack, and then remove the compound from underneath the tape by pushing down on the tape with a putty knife. Allow the compound to dry for 24 hours, sand the surface smooth, and then apply two coats of paint. Allow the paint to dry between the coats.