Entire books have been written on the subject of design principles, but knowing just a few will make you feel more comfortable when making decisions for your home.

			If you are decorating a small room, keep in mind that light colors on walls and ceilings, as well as wallcoverings featuring small patterns on light colors set against light-colored backgrounds, will make a room appear larger than it really is. A light-colored carpet or bleached wood floor, and pale-colored lightweight window coverings further enhance the sense of spaciousness. Reflective surfaces, such as lacquered furniture and mirrors also expand the apparent size of a small room. Paring down to a minimum of furniture and accessory pieces opens up a room, while low small-scale furniture creates a light open effect.
			Large rooms, on the contrary, can be cozied up and reduced in perceived size if they are decorated in rich intense colors, using wallcoverings and window treatments with large patterns featuring warm colors. Rough textures on carpets and upholstery and large-scale furniture items in darker colors will fill empty cold spaces.
			If ceilings are too high or too low, they can easily be brought into line: dark colors, such as deep blue or brown, used on a high ceiling will "lower" it. Similarly, light colors (or white) will "raise" a low ceiling.

Color is the key to "squaring up" long narrow rooms: Simply decorate the short end walls in a dark warm color to bring them forward visually and decorate the long side walls in a light color, so that they will recede and seem farther apart.

When arranging furniture in any sized room, be sure to take traffic-flow patterns into account. You don't want to be bumping into a chair every time you pass through a room to get to the next one. Anchor the furniture arrangement with one large-scale piece, such as a sofa or armoire and, for balance, add other pieces with less weight and size. Be sure that the eye has interesting things to focus on, both high and low in the room: you need a variety of heights. Choose a focal point around which the furniture will be grouped, e.g., a fireplace, attractive built-ins for a television or sound system, or a view out a window.

Finally, be sure to provide appropriate lighting. Rooms benefit from three types of lighting: general (overall ambient lighting); task (light directed onto small areas for such activities as reading or writing); and accent (to highlight desirable areas or create a mood) from wall-mounted sconces; for instance.