The key to successfully staging a long room is to not try to make it look like one continuous space. Instead, consider what uses the room may have and then break it up into a couple of different zones. For example, one side may be for entertaining guests, so it could contain a small couch and a couple of chairs facing each other with the fireplace as the focal point. The other side may be used for TV watching and lounging, so it would have a sectional sofa and a television cabinet. You can physically divide the two spaces by using a console table or a room screen, or you could just use area rugs with different patterns in coordinating colors to clearly define each space.
It's important when considering furniture placement to identify traffic patterns within the room. For example, you wouldn't want the main traffic route to the television area to cut through the entertaining area, so you would need to keep this in mind when arranging the entertaining area. You also wouldn't want to put the TV on a main traffic path, unless you want some agitated viewers. And here's an important design tip: In order to minimize the awkwardness of the room, don't face any furniture toward the short walls.