The most common design "mistake"...

...pushing all the furniture against walls, regardless of the shape of the room.
I see this all the time and I'm often called in on these rooms because my clients are unhappy with the feel and flow of the space. My number one tip: arrange the furniture in comfortable seating configurations and not against the walls.

Below are several before and after photos from a few clients. You will see the before images with furniture forced against walls and lacking comfortable conversation areas or even proper views to the television. The after rearrangements focus on comfortable rooms and logical seating arrangements, which pulls the furniture away from the walls.

Before:
After:
Before:
After:

Before:


After:

Try moving your furniture away from the walls. Does it revive your space; make you want to spend more time there? If you are worried about the furniture feeling like it's "floating", add an area rug to anchor the space. Try it for at least 48 hours to know how you truly feel about it.