Some designers shared their ideas:
1. Painting a room in a darker, cool-toned matte can make it feel like the walls are receding.
2. Floor-to-ceiling built-ins reduce visual clutter and create a more open, streamlined look.
3. Painting the ceiling the same color as the walls draws your eyes up and creates the illusion of higher ceilings.
4. A small-scale, simple wallpaper motif can make rooms feel larger.
5. Large scale furniture and rugs are associated with larger spaces and can ‘trick’ the eye to make a small space feel larger.
6. Breathing room around the perimeter of furnishings, and being able to completely walk around them, will make the space feel roomier.  (WSJ)