Every September I do the same thing. The black sunglasses go in a drawer, the tortoiseshell pair comes out, and suddenly every coat I own looks better. It isn't magic. Tortoiseshell is brown, amber, honey and near-black all at once, so it picks up camel, burgundy, olive and cream without trying. It's the warm version of a basic.

It also softens a face in low fall light in a way black acetate doesn't. Black frames can look severe against a gray sweater. Tortoiseshell looks like you meant it.

Start with shape. Round and oval frames are the gentlest, and they suit strong jaws and angular faces. The Lié Studio Lee is a slim oval at $270 and the easiest yes on this list. Celine's Triomphe oval has that slightly retro, slightly smug feel I love. Matteau's Eclipse is rounder and chunkier. If you want the heirloom version, Cartier's Panthère oval mixes tortoiseshell with gold-tone details and costs accordingly. The Oliver Peoples x Khaite 1989C is the one for anyone who likes a thin, bookish round.

One more reason to love it: tortoiseshell is forgiving. Smudges, a small scratch, a bit of wear on the bridge, all of it disappears into the pattern in a way it never does on glossy black.

Square and rectangular frames are for rounder or softer faces, or for anyone who wants to look like they have somewhere important to be. They also look more modern with a long coat.

I keep going back to the Saint Laurent SL 938, a clean square in recycled acetate at $420. The Dior Petit CD is narrower, which suits a smaller face. Bottega Veneta's Knot frame is a rectangle with a gold-tone knot detail you only notice up close. Jacques Marie Mage's Chelsea is the thickest and most sculptural-looking of the bunch.

A tip from too many hours in fitting mirrors: the top of the frame should roughly follow your brow line. If your eyebrows are floating above it, the frame is too small, so go up a size.

Square frames look best with a clean hairstyle, like a sleek bun or a sharp bob, and a coat with a strong shoulder. With a big fluffy scarf and loose waves, a round frame usually looks softer and more at home.

Then the shapes with attitude. Aviators in tortoiseshell feel warmer and less nineties than the metal kind. Bottega Veneta's Drop aviator is chunky acetate with a teardrop lens, while the Loewe Slim Light is a finer, lighter frame for every day. Chloé's Tubolar aviator splits the difference.

Cat-eyes lift the face. The Loewe Coil is a soft cat-eye rather than a dramatic flick, so it works for people who think they can't wear the shape. D-frames sit between square and round. Barton Perreira's Butzi is a classic Havana D, and Alaïa's version has a croc-effect texture that looks great with a leather jacket.

If you already own a round pair, pick from here or the square grid. The goal is one shape you reach for without thinking.

Sunglasses are one of the few places where spending more can change how something feels to wear. A well-made frame sits solidly on your face and the hinges stay tight. That said, you don't need a $1,500 frame to look polished.

What I'd skip: a pair with a big logo on the temple if you're only buying one, and strongly tinted colored lenses unless you already own a classic pair. Both date faster than the frame itself. I'd also skip ordering three shapes at once with a plan to return two. I have done this. The returns never happen.

If you take one thing away, it's this: choose your shape by your face and your coat, not by the brand. A $400 square frame that fits will get worn every day from October to March. A pricier pair that slides down your nose will live in a drawer. If you want to keep browsing, I also put together Best Sunglasses for Small Faces and Micro Sunglasses.