Measure from one side of the bi-fold door to the other and use the number to determine the length of curtain rod that you need. Measure from the floor to several inches above the door to determine the length of curtain you’ll require.
Install the curtain rod mounting brackets on either side of the door frame. Place them as high as possible to provide maximum hiding coverage for the door. Hold one bracket against the wall and make pencil marks through the screw holes. Repeat the process on the other bracket, at the same height.
Drill starter holes for the screws at the point of each pencil mark. Line the bracket up against the holes and screw it into place.
Thread a curtain of an appropriate length onto the curtain rod.
Mount the rod between the brackets and pull the curtain over the door to hide it.