Paint. Cheap and completely doable yourself, paint can revolutionize a room's energy and aesthetic. If you had light walls, consider going strong and dark, especially if you have beautiful molding or light flooring to work with.
Or go completely bold and dramatic with a highly intense hue.
Wallpaper. Go bold. For a powerful statement that will last through all of your moods, consider an art deco-ish pattern in a neutral mix, like this beautiful choice. Notice how little else is needed to make this space.
Showcase one piece. Whether you go out and get a centerpiece piece of furniture (Eames chair and lounger, I'm looking at you longingly), or simply slipcover an existing piece, choose boldly one piece to work around.
A piece like this bold leather speaks of casual luxury and can be a beautiful inspiration point.
Add art. Especially in limited square footage, art makes use of vertical space and can redirect the attention of the room.
Art just looks so sophisticated, especially when put up as a collection. And it's a great way to incorporate color.
A few simple pieces behind a couch will add instant elegance and a surprising change of perspective.
Renovate your mantle. While some mantle choices are intricate and require professional help, it is a susprisingly easy DIY project that can change the entire aesthetic of the space.
Covering the mantle with new materials will instantly update the room even if you do nothing else.
Get a rug. The simple addition of a rug can add warmth, color, and texture without moving another object.
A rug can draw colors together. Where there was floating furniture before, there's a distinct perimeter now.
Rearrange. The arrangement of furniture can make or break a space. Consider how you could completely turn the room and recreate it entirely.