Run a stud finder across the ceiling at the location where you want to nail the cove trim. Place a light mark on each ceiling joist using the stud finder.
Set the cove trim in the desired location. Check that the cove's outer corners are flush to the ceiling and wall. Drill 1/16-inch pilot holes through the cove trim over each ceiling joist 1/2 inch from the outer edges.
Place 6d finish nails into each pilot hole. Hit the nail heads with a finish hammer until they are close to the cove trim.
Set the tip of a nail set tool on top of each nail. Hit the back of the nail set tool to push the nail heads slightly below the cove trim.
Cover each hole with wood filler to conceal the nail heads. Allow the filler to dry and sand it lightly to match the cove trim.