Find and mark each joist in the ceiling, using a stud finder. Run pencil lines across the ceiling to show the positions of each joist, using a level to keep the lines straight.
Measure the edge of the ceiling where you're going to start, which must be one of the perpendicular edges to the joists. Use a miter saw to cut a piece of ceiling board to that length.
Set the board to the ceiling, along the edge, with the grooved side of the board facing the wall. Leave 1/2 inch of space between the board and the wall to allow for wood expansion. Shoot two nails through the face of the board wherever it crosses a joist, using a finish nail gun.
Cut the next board to size. Set its grooved edge against the tongue edge of the first board. Fit them tightly together. Shoot a nail through the edge of the board, at an inward angle, at each point where it crosses a joist.
Repeat for each new board. Build across the whole ceiling.
Use a table saw to cut the last board along its length, so it fits alongside the ending wall with a 1/2 inch of gap. Ceiling molding will cover the spaces.