It gives the illusion of space and depth. Frame your mirror nicely and position it to reflect something pleasing. If you feel that your mirror is too isolated, you can place a floral runner on top of it. If space permits, you can hang small paintings on either side of your mirror. Another alternative is sconces - either electric or candles on either side.
Art is always an answer for an empty entryway.
It's pleasant to look at and it's a good way to put a little of your self into the mix. If you have an old photo or painting, update it with a new frame or matting. You might have an entertainment center with a television, a piano, or maybe a fireplace. It depends on you and your lifestyle as to what you make the centerpiece of your living room. Once you've chosen the main focal point, start setting furniture around it.