Among the trends that the design world is all too happy to declare dead, the matching bedroom set, or suite as it's sometimes called, is right up there with flush-mount "boob" lights and popcorn ceilings. "Conceptually, it's very dated," San-Francisco-based interior designer Marea Clark says. "When every piece of furniture looks exactly the same, it feels a little lazy and makes for a boring environment."

Many companies still make these matchy-matchy sets, but they are unlikely to grace the pages of today's shelter magazines or designers' social media feeds. Instead, designers favor mixing an array of furniture finishes and styles for a more eclectic, collected look.

It hasn't always been that way: America's taste for the bedroom suite soured only recently. According to Alexis Barr, a design history instructor at the New York School of Interior Design, the idea of having matching bedroom furniture took off during the industrial revolution of the mid-1800s and remained popular through the 20th century, thanks to a mix of savvy advertising, expanded credit lines and a rising middle class.

"There was an attitude that if you've made it and you have your life in order, you can afford to buy things that go together," says James Farmer, an interior designer in Perry, Ga. "Now we think differently about these things."

But achieving the artfully mismatched look requires balancing furnishings in varying styles and materials. Pick too many motley pieces and your boudoir might have the aesthetic appeal of a roadside junk shop. So how do you master the mix? Here are the guidelines designers swear by.

Break up the set

Whether you've just inherited a bedroom set or you bought one 20 years ago and aren't ready to replace it, you can work with what you have to achieve a look with more personality. "If you already own a matching set, changing one significant thing can make a difference," Farmer says. "It's like buying a suit off the rack and adding a funky tie. That tweak is what makes it your own."

The easiest and least expensive items to swap out from a traditional suite are the nightstands. Adding a pair of bedside tables in a different finish or style can energize even the fustiest outdated set. And if there's a matching headboard, changing it to an upholstered one helps because it's one fewer wood piece in the room. "An upholstered headboard is a great opportunity to bring in some color or pattern through the fabric," Clark says. "Plus, they're comfortable; it's nice to have something soft to lean against in bed."

Vary finishes

When shopping for dressers, chests and nightstands, designers recommend mixing natural wood-tone finishes, which could include rattan and cane, with painted and metal ones to avoid the dreaded sea of all brown furniture. "If you have five different kinds of stained wood coexisting in your room, it can feel like a thrift store exploded," designer Shannon Claire Smith of D.C.-based Shannon Claire Interiors says.

For instance, Smith advises against buying nightstands in a light wood finish and a dresser in a similar but different tone because it might look like you tried to coordinate them and fell short of the mark. "Instead, I would combine the light wood nightstands with a black painted dresser, or do a burl wood dresser with lacquer-painted nightstands in a color," she says. "The possibilities are endless, just so long as the finishes are different enough to look like you did it on purpose."

That's not to say that you can't have two different wood tones happening in the same space. When Charlotte-based designer Charlotte Lucas works with more than one wood finish, she too aims for contrast. "It's easier to mix a darker wood tone, such as ebony, with a lighter burl wood piece because there's enough variation for them to complement each other," she says.

Consider scale and proportions

Smith says one of the trickiest proportions to get right is how the bed relates to the nightstands and vice versa. "Beds these days are awfully low profile and they don't have box springs like they used to," she says. "Platform beds can be a great look, but if you don't pay attention to that scale, it can feel very low slung, making the other furniture in the room feel off."

Ideally, you'll want no more than 2 to 4 inches between the top of the mattress and the top of the nightstand.

"You don't want to feel like you're reaching up really high or down low to set something on the nightstand next to you," Clark says.

The proportions get even more complicated when you have non-matching pieces on each side of the bed. Say you found the perfect antique desk and you'd like to use it as a bedside table. In that case, you should look for a nightstand, table or chest with a similar proportion and finish for the other side of the bed to unify the pieces. "The other rule of thumb is to make sure they are both the same height within an inch or 2," Lucas says. "If you have two radically different heights with identical lamps, it's going to look really off-balance."

If one bedside table is more than a couple of inches taller than the other, you can still make it work by choosing different lamps that hit at the same height. What's on both sides of the bed should carry a similar visual weight and have the same overall height.

Don't go overboard

Even the most eclectic interiors need balance and harmony. Bringing in too many stylistically unrelated pieces of bedroom furniture can produce a disjointed and chaotic result — the opposite of restful. "Your room might start feeling kooky if every piece is in a different style from a different period," Clark says. "Balance older, vintage or antique finds with newer pieces so it doesn't feel like a flea-market hodgepodge."

Designers agree the key is to pick one dominant style to anchor the room, then pepper that with a few contrasting pieces in other styles. For instance, in a room of mostly modern furniture, one or two over-the-top French or antique pieces can break up the monotony. "Similarly, if you have all traditional furniture with classic lines, throwing in one sculptural, midcentury item is a great way to make the room feel instantly cool," Smith says. "Drawing that juxtaposition is key to making the space unique."

Farmer adds: "There's a gift that you're giving yourself when you appoint your bedroom. It's your space, so be unapologetic about expressing your style."

Michelle Brunner is a writer in D.C. who covers interior design and culture.