Cut drywall pieces to fit the corner
Fasten drywall securely to studs
Leave a small gap at floor and ceiling
Apply drywall tape to the corner
Use paper tape for inside corners
Use corner bead for outside corners
Apply a thin coat of joint compound
Embed the tape or bead into the compound
Smooth out excess compound
Let the first coat dry completely
Apply additional thin coats as needed
Feather each coat wider than the last
Sand lightly between coats if needed
Finish with a final smooth sanding
Prime and paint after drying