The living room affords you perhaps the most opportunity to really express your creativity and personality. That's why I've put my big desk front and center in the room. No, it's not the fact that there is no other place for it. I find that another nice way to decorate a room is with electrical cords. Run as much phone cord, extension cord, and cable around the base of your walls as possible.
Ornamentation is very important for a living space.
While my art hangs nicely upon all walls, I found that those empty spaces between windows, over doors, on my archway, etc., were looking a bit naked. So to combat that, just hang random objects. Hang it up. Also make sure to both forget to take down a photo of you and your friends smoking and leave your bong out when your mother next comes to visit. She'll love the extra attention to detail.