It is not at all difficult to stick polystyrene tiles on the ceiling. The first stage, as in all other repair and final work, is the preparation of the surface. It is necessary to remove the old coating, repair cracks and chips and make the surface even. It is better to start gluing tiles from the center of the room. So the ceiling will have a more presentable look. In order to find the center of the room, you need to pull the threads along its diagonals. The point of their intersection will be the center from which you should start. If the installation of tiles from the center is impossible for any reason, you can start from the corner or from the interior doors. Having determined the central point of the ceiling, you need to take the tile, apply glue to it and place it so that one of its angles is located at this point. All subsequent tiles are glued parallel to the first, as tightly as possible to each other.
It happens that the tiles are slightly different in size. Therefore, it is best, before applying glue, just attach dry tiles and evaluate how suitable and if necessary to cut it or replace another. The ceiling plinth will give the ceiling a complete look, and the stucco molding installed in the places of attachment of the chandelier or lamp will make it more elegant.