As your house settles the walls will crack from the doors and windows (typically the corners). No matter if your walls are made from plaster or drywall you can repair them.
Make sure the area is ready to sand and paint. And make sure you use paper tape, as it is stronger than fiberglass tape for this type of repair.
For cracks that are deeper than ¼ of an inch. Remove the loose materials and use a crack filler that is quick-setting to be sure the area is on the same level as the wall. Then continues as usual.
Back the shallower cracks: Remove all the loose material from the crack. Use masking tape to protect the wall studs.
To make sure you don’t get air bubbles underneath the tape get the tape wet with water and then lay it over the crack. Squish the extra compound and air from underneath. Apply another layer of crack compound and feather it from all sides at least 2 inches on either side. Let it dry.
Apply another coat or two of the compound and feather it 6-7 inches on either side. Smooth it using a 12-inch taping blade. Let it dry completely and sand it. When it has been sanded smooth you can paint!