With cooler fall weather, we’ll soon be turning off the air conditioning and opening windows. As breezes set curtains fluttering, it’s the perfect time to consider the way your windows are decorated.

“Dressing windows is one of the most impactful ways to give any space a designer edge,” says Brian Patrick Flynn, an interior designer and founder of decordemon.com.

The freshest looks now, according to Flynn and interior designers Betsy Burnham and Mallory Mathison, are all about simplicity, softness and fuss-free design.

•  Simple hardware: “The skinnier the rod, the fresher the room will look,” says Burnham, founder of Burnham Design in Los Angeles. “Just a skinny rod with tiny rings is all you need. It’s very graceful. … When I see 2-inch and 3-inch wooden rods and clunky rings now, it looks so dated.”

Mathison, who is based in Atlanta, agrees: “People are moving away from window treatments with cornices and valances.” With a basic curtain or Roman shade, she says, you don’t need to worry about “anything collecting dust or dirt, or kids wrapping themselves up in bunches of fabric.”

•  Sheers and naturals: Mathison increasingly prefers to use sheer curtains on their own, rather than pairing them with thicker draperies.

Adding a thin, organic cotton lining to a sheer curtain panel adds a bit of privacy, but keeps “that sort of flowy, gauzy look,” she says. “It’s a soft little frame for the window and there’s no distraction with it being a heavy fabric.”

•  Only the fabric you need: A few years ago, Burnham says, many designers favored piling on fabric to create dramatic windows. Today, there’s a spare approach.

“We’re not swagging. There’s no puddling of fabric on the floor anymore,” she says. Now, it’s best for fabric to “just kiss the floor.”

The same rule goes for Roman shades: “A simple, pleated style, not too much fabric” has become more popular than billowing shades.

And phony curtains are definitely out: “Don’t put up two panels that don’t actually close,” Burnham advises.

•  Custom look for less: It’s increasingly easy to get the look of made-to-order window treatments without the cost. All three designers suggest buying pre-packaged curtain panels, then having them custom lined and hemmed to fit your windows.

“I stick with linen and cotton,” says Flynn, “then drop them off to a seamstress to be lined so they hang nicely. Next, I have the tops sewn ‘soft top’ style, which is a straight stitch that gives a casual, relaxed look. Then drapery hooks are added. The cost is anywhere from $25 to $125 per panel, depending on the type of pleat and liner used.”

Or buy several yards of fabric and have a seamstress make simple panels, rather than having curtains done by a custom window treatment retailer. “The difference in cost, if you have the work done by someone who normally tailors clothing, is going to be noticeable,” Burnham says.

If you prefer shades to curtains, Mathison says to apply the same strategy: Buy a plain white cotton Roman shade, she says, then attach a flat ribbon trim across the bottom border or even a cotton pompom fringe for a child’s room. The look is simple and clean, and the expense minimal, but you’ve added a dash of color and texture.