In a high-ceilinged room, use an oversized chandelier. De-electrify it and just use it with candles so it becomes a piece of sculpture rather than a glaring light fixture, and it anchors the space. In a small room, choose a bold, big-pattern print and cover everything in it, the French way: walls, curtains, upholstery, et cetera. It gives the room vibrancy and glamor. Also, use large, but fewer, pieces in a small room—like a sofa that may seem too big—so it feels luxurious. In a large room, use smaller-scale pieces to create several areas and bring the space more to human scale.
I love the way that Dunham plays with scale in the room above, using a bold patterned print for the walls and matching sofa. It's an important lesson to remember when redecorating a room — keep scale a playful, and important, consideration.