Lines should provide variety without confusion. Lines can provide direction or movement of the eye throughout a room. Shape and size. Use a variety of shapes for interest. Make sure your furnishings are in pleasing proportion to one another and to the room.
Different textures lend different feelings to a room.
Use patterns to add interest. Start with a pattern and use its colors throughout the room, or choose a pattern that coordinates with the room's existing colors. Repeat patterns in the room and don't be afraid to mix patterns. Keep light bulbs clean for maximum light. Replace lampshades when they become dark and yellowed.