There's no shortage of interior design advice online, but it isn't always easy to tell what a particular space actually needs. Some mistakes barely affect the result; others only surface during construction and change the original design completely, usually for the worse. At deZZign we've seen this firsthand, so we know what we're talking about. We catch exactly these critical errors early with 3D visualization of the design project, before construction starts. Sometimes we inherit projects abandoned by previous designers and have to correct the drawings and walk the builders through what changed.
Here are 12 rules from respected designers around the world that show what NOT to do.
1. Pushing All the Furniture Against the Walls
According to Young Huh of Young Huh Interior Design, there's no need to line every wall with furniture. Pulling pieces into the room makes it livelier and better for conversation: a sofa and chairs facing each other create a natural seating group. Sketch a layout on paper or a tablet and refer to it as you arrange. If you're completely out of ideas, start with a couple of chairs in the middle of the room and build out from there.
2. Forgetting About Lighting
Lighting is one of the most important elements of an interior; it changes how the whole space looks and feels. As Alfredo Paredes of Alfredo Paredes Studio suggests, sometimes swapping a few bulbs and adding a couple of good wall sconces transforms a room without any renovation. It's best to leave lighting to a professional, but if you're doing it yourself, remember the three layers: ambient light for the whole room, task light for work surfaces and reading, and accent light for art, textures, and architectural details. Read more in our article on interior lighting.
3. Not Measuring the Space
In interiors, "eyeballing it" doesn't work. Nobody wants to pay to replace furniture that won't fit through the door or blocks a walkway. Always measure, preferably more than once, and measure not only the room but also the doors, elevator, and stairs the furniture has to travel through.
4. Bringing In a Designer Too Late
Too often, clients approach a designer after they've already hired a contractor, and sometimes construction has already started without a clear plan, even though skilled builders need drawings to work from. It's one of the biggest problems we see. According to Mandy Cheng of Mandy Cheng Design, the designer should first get to know the space, then discuss ideas and possibilities, and only after that should the search for contractors begin.
5. Choosing Furniture That's Too Big or Too Small
A harmonious room depends on scale, and getting it right is hard even for experienced designers; without it, furniture looks out of place. A useful rug rule: either all the legs of the sofa and chairs sit on the rug, or at least the front legs do, so the rug anchors the seating group instead of floating in the middle. A rug that stops short of the sofa almost always looks too small.
6. Putting Looks Ahead of Comfort
Never buy furniture without trying it in person. Sit or lie on the sofa, feel the fabric, and check the color in daylight. Furniture has to be functional above all. Avoid choosing purely on looks or price, which happens far too often, sometimes because unscrupulous sellers or designers talk trusting clients into it.
7. Hanging Art in the Wrong Place
Art should hang at eye level; what's the point of a beautiful piece you can't properly see? One of the most common mistakes is hanging art too high, as if that will make it feel grander. The rule of thumb galleries use is to center a piece about 57-60 inches (145-152 cm) above the floor, and above a sofa to keep the bottom edge 8-10 inches above the back. And don't hang art on every wall; it quickly becomes overwhelming.
8. Not Trusting Professional Advice
Don't be afraid to try something new. An interior benefits when you listen to a designer's seemingly unconventional suggestions, within reason, and bold choices are what make a space unique. Francis Merrill of Reath Design suggests gathering everything you like - objects, colors, samples - and looking at them in different light and, if you have time, in different seasons. That shows whether they really suit you and whether the combination will wear thin.
9. Maximalism Without a System
Don't overload a room with prints and patterns. Stick to a few core colors: the less unnecessary stuff, the more open the space feels. The same goes for furniture and decor.
10. Forgetting About Balance
A room without balance feels unfinished. The simplest route is symmetry: mentally divide the space in half and arrange things so both halves carry equal visual weight. But balance doesn't have to mean mirror symmetry; a large sofa on one side can be balanced by two armchairs and a floor lamp on the other. Asymmetrical balance often feels livelier and more contemporary.
11. Overdoing Accent Walls
Accent walls are risky: they can make the other walls look dull and throw the room off balance. If you want one, give it a reason - the wall behind the bed or sofa, a niche, a fireplace - and repeat its color or texture somewhere else in the room.
12. Skipping the Rug Pad
A rug pad is a small expense that pays for itself. It keeps the rug from slipping and bunching, which is a safety issue, protects the floor from scratches, dampens footsteps, and extends the rug's life. Over radiant floor heating, choose a thin pad rated for it, and in damp spaces pick a breathable one so moisture doesn't get trapped under the rug.
Mistakes We See Often in Seattle-Area Homes
To the universal rules we'd add a few that are common in the Pacific Northwest: relying on a grid of cool-white recessed cans that makes gray winter days feel even grayer; skipping a real entry or mudroom, so wet coats and shoes end up in the living room; dark walls in north-facing rooms that already get little daylight; and outdoor-looking materials inside that don't stand up to constant damp traffic. All of these are easy to fix on paper and expensive to fix after move-in.
Frequently Asked Questions
What is the most expensive mistake? Starting construction without a design: reworking wiring, plumbing, and partitions after finishes are in costs many times more than the drawings would have.
How high should art be hung? Center it about 57-60 inches above the floor; above furniture, keep the bottom edge 8-10 inches above the sofa back or dresser.
Do I need an accent wall? Not necessarily. It works when it highlights an important zone, especially if its color or material is echoed in the decor.
How to Avoid Most of These Mistakes
Most of these 12 mistakes come down to the same fix: the right sequence of work. Accurate drawings for the design project up front, thoughtful furniture selection and material selection matched to the actual space, and genuine project support through construction - not correcting what was already built wrong. If you're not sure who you actually need at the start - an architect or an interior designer - we've written a separate breakdown of that difference. And the whole process starts with a genuine interior design project.
Most of these mistakes are prevented by working drawings, not renderings. For what a complete set looks like, and what a single misplaced outlet actually costs, see our walkthrough of a real 68-sheet design project.
