Vertical lines have a stately presence. Edge a group of picture windows with long sleek drapes. Think of the presence columns make in a room or a building facade. Your eyes are drawn from floor to ceiling, absorbing the full view.
Horizontal lines provide a greater sense of comfort. Think landscapes and sunsets. Top windows with a clean-lined valance or cornice to bring the room extra warmth.
Diagonal lines indicate movement and change. Such angles should be used sparingly, but can have an empowering and bold effect.
Curved lines provide a sensual and soft feel. Rounded swag or voluminous drapes can provide a room with richness the brings comfort.