Start with wall color and window treatments. Select wall color, wood trim color and curtains you like. You can pick out one or more sofas to fit well in the space. Build the rest of the room layout around the sofa area. Add a couple of chairs, a coffee table and appropriate end tables. Choose artwork that you absolutely love that picks up colors used in the furniture. Never hang artwork that is simply selected because it fits because paintings or prints will affect your mood the whole time you're in the living room.
Mix different materials. Use high-tech pieces along with traditional, for example. You can use metal end tables with a cherry coffee table and leather sofas, for example. Different textures and materials make the room look better designed than picking out showroom-style groupings. Buy one or two accent pieces or tables made of marble, rustic wood or glass.
Keep the room clean looking. Don't use too many different colors. Paint the walls light parchment, and use brown leather sofas with black tables, for example. Avoid using many shades of brown or green in the room. Think of creating the room for a photo shoot versus using an eclectic mix of items that look overly casual.
Make all of the metal items in the living room match. For example, use dark brown metal on overhead light fixtures and lamps, along with dark brown metal on end tables and the coffee table. Don't use chrome light fixtures with gold-metal lamps or bronze-finish lamps with a black metal overhead fixture.
Plan the room from every angle. If the living room is surrounded by a porch on two sides, for example, ensure that the furniture grouping looks good from outside areas too. Place the back of one sofa to face one porch and the back of another sofa to face the other porch area. Leave 4 or 5 feet between the sofa and the windows next to the porches. Add sofa tables with plants. Look at furniture groupings from any other entrances to the living room to ensure everything is balanced.