A lot of cracks in drywall happen at corners of openings such as window and doors. These can result from the building settling but they are usually caused by shifting framing members which may be missing fasteners or don’t have enough fasteners.
So how can we fix them? Let’s consider, for example, a crack that follows along a framing member down from the corner of a window. Using a utility knife, create a narrow v-shaped groove along the length of the crack. Clean out any drywall dust from the groove.
Next put in fasteners (preferably drywall screws but drywall nails will work too) along each side of the crack and space them about 6 inches apart and stagger them so they are not across from each other. Be sure to counter-sink the fasteners or they will show up as a nail pop. Now you’re ready for joint tape (preferably reinforced fibre mesh as it is stronger).
Apply the tape along the length of the crack and a little beyond each end. Drywall compound (mud) is added next. Use a wide drywall knife so you can spread the mud out to about 10” or 12” on either side of the tape. This will give you a wide enough area to feather out the edges and sand the surface so it blends in with the existing wall. Two thin coats are better than one heavy coat as it will shorten drying time and may reduce the amount of sanding. If you are satisfied with how it looks, you are ready to paint.
TIP: When it comes to sanding small areas like this, there are small sponges on the market that already have a sanding block in them. If you moisten the sponge a bit, it will catch a lot of the dust and make clean up easier and it helps smooth out the edges of the repair.