Keep furnishings to a minimum to avoid clutter. Use large-scale prints and furniture to fill a space. Modify room proportions by your choice and placement of colors. A long narrow room appears less so if end walls are darker than are the side walls. A grouping of furniture near the center of the room also helps cut length.
Color can make a square room seem less so by making one wall lighter than are the other walls.
Ceilings should be lighter than walls unless you wish them to appear lower. Architectural features and materials. Doors, windows, and other features call attention to themselves if they contrast with walls. Use contrasting colors only if you wish to emphasize the feature. Match others with the wall.