One. Furniture placement is everything. It make spaces feel right and with just the right layout you'll have beautifully designed and functional spaces. Don't line your walls with furniture. Even in small spaces, bringing things towards the center of the room or angled will make your space feel bigger. Consider balance in arranging pieces. Put your largest or tallest piece on the biggest wall. Arrange furniture so you vary tall and short pieces around the room. It's smart to leave at least 18" between pieces of furniture so you can walk through and around easily. I prefer 24" however most people don't have that much space.
Two. Use the best lighting possible. So many times we consider the ceiling fixtures installed by the builder as the only ones available. That often makes us not use a space because the lighting is poor. It's really easy to change a fixture from something dated to something cool and artistic. You can even transform a recessed fixture into a pendant light. Don't forget to add fabulous table and floor lamps and consider tucking LED accent strips or up lights in a dark corner. Adding wall sconces is easy and you can create a fabulous design statement with relatively inexpensive fixtures. The easiest fix....put your ceiling lights on dimmers so you can change the level of lighting and mood of your space as needed.