Are you making these design mistakes?

Your flat-screen TV may fit perfectly over your mantel, but that doesn't mean you'll enjoy watching it there. This placement can be uncomfortable after a 30- to 60-minute show because you have to crane your neck up to see it, says De Vargas. For easier viewing, make sure the TV is the same height—or within a five-inch radius—of your eye level when sitting down.

If only modern furniture felt as good as it looked. Sleek-looking sofas are sometimes too firm or designed in a way that offers little or no back support. An easy fix that de Vargas used on a tufted leather sofa? I added two large 26-by-26 pillows with a few decorative ones in front to make them more cozy, she says. Wooden benches—another popular choice for modern dining tables—can also be a bit stiff for a dinner party. In that case, De Vargas suggests adding cushions to the benches or buying a contemporary style that features built-in cushions like the Bergman Bench from Jonathan Adler.

Tolerating nonstop AC or stuffy air because you're worried a fan will create an eyesore? Breathe easier. New retro-chic table fans keep you cool without ruining your decor, says De Vargas. (Check out this fashionable fan from Target.) For even better air circulation, a streamlined ceiling fan in the same shade as the actual ceiling will blend right in so you hardly notice it.

You may love a white Flokati rug, but if you have kids, you'll likely spend more time cleaning it than enjoying it. I always tell clients to opt for a darker rug in kids' rooms and high-traffic areas, says De Vargas. Something really busy, with multiple colors—like a zigzag pattern—is even better, she adds. I'm a big believer in Persian rugs because they have lots of different designs and colors. As for furniture, stain-resistant fabric is the only way to go.

Houseguests can cramp your style if your spare bedroom is used for more than just visitors. Home offices often double as guestrooms, so getting a desk that closes up can be a great way to make the most of your space, says De Vargas. Another option: Turn a walk-in closet into an office and buy a wardrobe for guests to store their clothes. And ditch the air mattress and save space with a daybed that has a trundle underneath for your guests. Air mattresses are for teenagers and teenagers only, says De Vargas.

Cooking can mean hours on your feet, leaving you exhausted even before your first guest walks in the door. Adding a waterproof floor mat in front of the sink or kitchen counter can help save your soles, says De Vargas. Worried all the styles are tacky? Not so. Check out the array of designs from Wellness Mats.

Your weatherworn wood patio furniture may look shabby chic, but splinters, spiders and rust could put a damper on those al fresco dinner parties. Uncovered, outdoor furniture will get damaged and fade and fall apart—even saltwater and moisture in the air can lead to rust, says De Vargas. Store removable cushions when they're not being used and buy a cover to keep furniture protected. Bonus: Thanks to end-of-summer sales, now is a great time to invest in furniture covers, says De Vargas.

It's easy to get caught up designing the perfect nursery and forget your baby will only be little for so long. Look for cribs that convert into toddler beds and bookcases and shelving units in modular and stackable styles, so the furniture grows with your child, says De Vargas. Pieces with rounded corners and different heights prevent kids from hurting themselves and allow them to reach certain things—but not everything. Breakable lamps and picture frames sit safely up top, while stuffed animals, toys and books can stay down low for easy access.