Ok the scene looks setup quite well all you need is more contrast in the image, everything has the same light feel to it. Dunno if u using Vray or what but try putting your secondary bounces down a bit, the re should be more light coming from the direct light than the ambient light. Also the colour tone doesn't help, it makes it feel very cold. Having said that if this is a still image and not an animation sometimes it's much faster to get a decent render and photoshop the image to get the atmosphere you want. Lemme see what i can do with yours, now bear in mind i don't have your model or lighting situation so it's just gonna be a quick mockup of what i would do, by playing with colur tones and brightening and darkening some areas. I know it sounds like cheating but believe me sometimes it's faster and less of a hassle that way especially if u're running out of time. If it's a project which is gonna go through lots of iterations and renders then it's worth the time to get the lighting just right. In that case hide all the furniture except the big masses like the sofas and try very small renders to test the lighting situation, u wanna try have one main bright light coming from the exterior casting strong shadows and with a touch of yellow/orange to make it warmer. U also wanna brighten the exterior cos if u look at a photo of any interior with a window u'll notice the exterior gets very overexposed, also u can add a glow in photoshop from the window opening. Hope any of this helps.
