Horizontal lines will give the effect of relaxation as well as breadth. If you wish to achieve a restful room I would suggest you stress the use of horizontal lines in your wallpaper, drapes, lampshades, picture arrangement, upholstery and furniture. These horizontal lines would predominate in a room that is informal. Vertical lines will express formality and masculinity. For example a man's bedroom would stress vertical lines, while a feminine bedroom would avoid vertical lines in plain or patterned surfaces.
Diagonal lines are restless and dynamic and give the feeling of instability.
Broken lines will express gayety and animation. You might use broken straight lines in pillows or cushions to show pleasing variety. Curved lines will promote softness, being lighthearted in appearance and have an effect of being cheerful. Be careful to not overdo curved lines as they can appear ornate. Forms will convey fulfillment and completeness.