Remove all of the free-standing items from the room. Cover floors and other surfaces with plastic sheeting. Hang more plastic sheeting over the walls with painter’s tape to prevent paint splatters.
Apply shellac-based primer to the ceiling using a ¾-inch nap roller on a telescoping handle. Roll on the primer in long, even lines that overlap as little as possible. Let the single coat of primer dry overnight.
Paint the ceiling with latex-based ceiling paint, applying the paint in long lines in the same way you applied the primer. Let the first coat of paint dry for a full day, and roll on a second. Do not simply try to use one thick coat of paint, as the popcorn texture will become heavily saturated and will drop away from the ceiling.
Wait 24 hours to ensure the ceiling is very dry. Remove the plastic tarps from the floors and walls. Return the furniture and other items to the room.