Sometimes it seems as if what constitutes good design is purely subjective. One person rejects any home with French Provincial furniture. Another will look only at ultramodern interiors. And then there’s the guy with the Leg Lamp.

But if taste sometimes seems arbitrary and fast-changing, there are core principles of all good interior design that are timeless, says Attila Lawrence, head of the interior architecture program at the University of Nevada, Las Vegas.

Keep these three basic design principles, plus functionality, in mind as you view homes, and you’ll be able to help sellers optimize their home’s appeal and help buyers look past shag carpeting and poor furniture layout to see a room’s potential.

1. Balance

Balance means using furniture and other objects to make each part of an arrangement roughly equal in visual weight so that one area harmoniously complements the other. Perhaps the easiest way to achieve balance is through symmetry, where one side of a room exactly matches the other. It’s balanced, but it’s also formal, says Lawrence, which may not be the look that appeals to a specific buyer.

Balance can also be asymmetrical, with one large piece of furniture offset with several smaller furniture pieces or objects. “You want to achieve a visual symphony in which every ‘note’ is appropriate to the function of a room and nothing is distracting; it’s like a great musical composition,” says Lawrence.

2. Harmony

Harmony in a room occurs when all parts of the ­arrangement — from furniture to accessories to wall color — combine to create a pleasing whole. An easy way to achieve harmony is through repetition—in color, texture, or shape. So a green chair might be echoed by green in the draperies and green pillows on the sofa. Repetition doesn’t necessarily mean duplication, however. You can change color intensities, for example, from a deep to a lighter hue, and still gain a sense of repetition.

But don’t go overboard; too much repetition can make a room feel predictable and boring. “An orchestration of related elements helps us comprehend and connect objects in relation to the space. Without that connection, the space seems to lack a sense of unity,” says Lawrence.

3. Emphasis

Every well-designed room needs a focal point — a fireplace, a terrific view framed by a compelling window treatment, or a powerful painting — to draw the eye into the space. Large spaces may need several points of emphasis.

“It’s the contrast between what is emphasized and what is not that creates interest in a space. Without a focal point, there’s no place for the eye to rest and the interior seems uninteresting,” says Lawrence. “With a focal point, you can immediately respond to the aesthetics of an interior space.”

4. Functionality

In a home, the adage “form follows function” (made famous by master architect Louis Sullivan) should be the golden rule. A room where children will play and the family will gather needs furniture with durable fabric, a layout with space for blocks or homework, and relaxed furniture styles to fit the room’s many functions.

“Everything in a given space should be appropriate to and support the experience of what will take place there,” says Lawrence.