If You Want a Traditional Look
Pillow number and placement: Two or four large pillows arranged on either side of a sofa impart a sense of symmetry and order.
Shape and size: The right size depends on how big your sofa is, but for eye-pleasing proportions, try pairing square pillows measuring 20 to 22 inches across with smaller squares or circles.
Fabric: Velvet and silk look great in a classic setting. Layering a variety of textures, patterns, and colors keeps things lively. "Sometimes more is more," says Flesher. To help patterns such as paisleys and florals commingle without looking fussy, Donovan suggests pairing a busy pattern with a simple one, like "a complicated plaid with a large floral that's just two or three colors." A print and a coordinating solid will work, too.
Trim: Save the big trim, like tassel fringe, for larger pillows "to give them more oomph," says Scott Salvator, an interior designer in New York City. Small pillows look best with slim trim, like braid or cord.