Cut drywall sheets to fit the corner
Fasten drywall securely to studs
Leave a small gap at floor and ceiling
Apply joint tape along the corner
Use paper tape for inside corners
Use corner bead for outside corners
Mix joint compound to a smooth consistency
Apply a thin coat of compound over the tape or bead
Press tape firmly into the compound
Remove excess compound with a drywall knife
Let the first coat dry completely
Apply a second thinner coat
Feather the edges wider each coat
Sand lightly after drying
Apply a final skim coat if needed
Sand smooth after the final coat
Prime before painting