Paint the long wall a warm, neutral color. Try a cream, taupe or soft yellow for your wall color. You can even vary the shade of the color you choose for the long wall. Paint the bottom half of the long wall the darkest shade. The next ¼ of the wall should be slightly lighter and the top ¼ of the wall should be the lightest of the three shades and should match the color of the ceiling. This will draw the eye up and down, instead of from side to side.
Arrange your furniture to break the long wall into sections. Try placing your sofa, love seat or bed perpendicular to the long wall to create sections. Or use a bulky piece of furniture such as a hutch, entertainment center or piano to break up the monotony.
Add floor lamps to give the long wall height. Make sure the lamps are in contrasting colors to the wall. Many floor lamps are adjustable so you can vary the height yourself. Direct the light from the floor lamps upwards. Place a tall plant between the furniture and the wall to add height. A tall grandfather clock against the long wall also adds height.
Create a faux window on the long wall. Use fabrics to add texture, depth and dimension to the long wall. A bulky valance with heavy draperies will help to break up the long wall. You can even paint a mural of an outdoor scene on the long wall, should you want to open the curtains.
Add a faux fireplace. Fireplace kits are available at decorating and home improvement stores. Add all the fireplace accessories such as a decorative basket for storing wood and fireplace pokers and shovels. You can even paint a faux fireplace directly on your long wall.