In modern homes, this is certainly unlikely to be possible due to space limitations, though traditionally, fireplaces were considered to be the best central element to a living room! But it's important to remember that the intention of your living room is being inviting to people, to have them to feel comfortable and relaxed, and stimulate good conversation. So even without a central fireplace, making the fireplace some sort of focal point will also work well. Mirrors are a wonderful tool to enhance Feng Shui in a living room. They bring light into darker areas and might reflect aspects of the area that visitors might not otherwise enjoy. Mirrors make rooms look larger (and lighter) and very usefully, they will reflect the door, so any seating that cannot face the door can still have the door visible through the use of mirrors. The best placement for your mirror is where it could possibly reflect a beautiful view, but once again, we must adapt this principle to modern homes and cities.