The first rule of design is: everyone's taste is different. But interior designers know so much about trends and style that they can't help but make some judgments (good and bad!) when they enter someone's home. In case you have a design expert roaming your halls, or if you are just curious how to make your house completely designer-friendly, we put together a list of what professionals actually notice when they walk through the front door.

HOW THE ROOM IS LIT.

"I'm really sensitive to lighting," designer Vern Yip says. "Nine times out of ten, I think when people walk into a room and they like the ambiance, it's because the lighting has been done correctly." According to Yip, this mean the room has a variety of light sources, including recessed, sconces, hanging fixtures and more.

THE LAYOUT OF THE ROOM.

When designer Scot Meacham Wood first visits a client's home, he always picks out what isn't working (usually the layout and room function). Why? So he can offer solutions, of course. "If we're doing construction, I look for architectural errors that we could fix, like poorly aligned doorways and oddly placed overhead lighting,"

IF THE SOFA IS AGAINST THE WALL.

Within minutes of walking into a room, Sarah Vaile of Sarah Whit Interior Design says she's already reconfigured the furniture in her head. "Nothing drives me crazier than a sofa against the wall in a large room," she says. Often, she finds her clients have good taste, but just don't know how to lay the pieces out.

WHETHER OR NOT THERE ARE FLOWERS.

Small accents can say a lot, which is why CeCe Barfield Thompson of CeCe Barfield Inc always takes note. "Little touches help a space feel like a home," she says, like flowers by the door, an organized-but-used entry way and a easily accessible bar, of course.

THE NUMBER OF PILLOWS ON THE COUCH.

In this case, Vaile says more is always better: "It drives me crazy when there are only two sad throw pillows on a sofa." Not to mention that multiple throws will make your couch so much cozier.

ALL THE LITTLE ITEMS

The smallest items in the room catch interior designer Eche Martinez's attention: "I'm obsessive about spaces being uncluttered and personally prefer minimal styling," he says. "So many times I walk into beautiful homes only to encounter endless tiny memorabilia sitting on the mantle gathering dust!" Permission to ditch those 10-year-old crafts, granted.

HOW SHELVES ARE ARRANGED.

Apparently, how you organize your books says a lot — at least, according to interior designer Frank Bostelmann. "Books stacked in piles generally show that no one is reading them and they are there as decorative props," he says. Personally, he likes his collection of hardbacks to be more accessible.

ALL THE WOODWORK ON THE WALLS.

We're talking the trim, crowns and other millwork casings on your walls. "Investing in well-proportioned trims can establish the look and foundation of a room," says Bostelmann. But a cheap stock trim or casing can't be hidden, he warns.

IF THE CURTAINS TOUCH THE FLOOR

Sure, it seems like a minor detail to you, but many designers said they (unfortunately for us) notice gaps when they exist. "I am always hyper aware of things that are out of scale," says Berry. Fair enough.