Divide the long wall into different space with molding and paint. Determine where you want to divide the wall. Install a wide piece of decorative molding in a vertical fashion on the wall at the point where you want to make the division. Paint the wall on either side of the molding in two different colors. Select colors that coordinate to create a unified look, or choose contrasting colors to create a clear division.
Use furniture to divide the wall. Position a large piece of furniture -- a sofa or a china hutch, for example -- so that one end is pushed against the wall. When using furniture to divide the room, arrange the piece so that the front is facing the side of the room that you intend for it to be used in. For example, if you're using a sofa, position it so that the seat is facing the living area.
Set up a decorative room divider. Hang a curtain from the ceiling across the room. Choose a neutral curtain that works with the decor on either side of the wall. Set up a decorative shoji screen on the floor so that one end is touching the long wall.