Now the long sleeves and the maxis. Vogue's fall guide names plum, burgundy, saffron and terracotta as the shades for the season, and I think of this group as the place where those colors go to work. A long hem and a covered arm also mean you need very little else: a small bag, a good shoe and a coat for the walk from the car.

By Malene Birger is the busiest label here, with the Parisa Silk Maxi Dress in a dusky plum and the Beatriz Long-Sleeve Cotton-Blend Knit Maxi Dress in wine, a knit that would carry you through a cold evening. The Silvia Tcherassi Lina Gathered Silk-Blend Maxi Dress in red and the De La Vali Daira Georgette Gown in fuchsia both have long fitted sleeves and a flared hem, so they move when you walk. The Stella McCartney Satin Cutout Detail Gown in burgundy is the sharpest shape, with a high neck and wide sleeves.

If you like jersey, the Aje Selah Jersey Maxi Dress in chocolate is ruched at the waist, the Tove Eira Ruched Jersey Maxi Dress in olive is gathered through the body, and the Significant Other Luna Draped Jersey Open-Back Maxi Dress in forest green is the simplest of them, with the back doing the work. The Erdem Printed Long-Sleeve Gown in navy is the print for the friend who never wears plain.

Then the romantic end. The L'IDÉE Empire Gown in aubergine has a pleated skirt and a tie at the neck, the De La Vali Clementina Ruffled Lace Maxi Dress in brown is lace with ruffled cuffs, and the De La Vali Florencia Chiffon Maxi Dress in brick red has a cape over the shoulders. A sheer sleeve or a cape looks lovely in photos but can feel cold outside, so bring a coat for the walk from the car.

If the invitation says black-tie optional, Emily Post says guests have a couple of formal options: a formal evening gown, a shorter cocktail dress or dressy separates. Any of the long gowns here would sit comfortably in that first category.

Velvet is the fabric I trust most in October and November. Britannica defines it as a fabric with a short, dense pile, with a soft, downy surface formed by clipped yarns. That pile is why the color looks so deep: light sinks into it instead of bouncing off, and a burgundy or green reads richer than it would in a flat fabric.

Leo Lin has two, and they could not be more different. The Florence Ruffled Velvet Maxi Dress in dark green is strapless, gathered at the side and long, the one I would wear to an evening ceremony. The Ariel Bow Velvet Mini Dress in black is short and full skirted, for a cocktail-hour wedding. The SIEDRÉS Adeline Gathered Velvet Maxi Dress is printed velvet with short sleeves, and the Alfie Maia Stretch-Velvet Midi Dress in gold is crushed velvet that catches the light.

For something shorter, the Khaite Benji Velvet Mini Dress in black is a clean shift with short sleeves, and the Rodarte Velvet-Trimmed Silk Crepe Bias Mini Dress in mint uses velvet only for the bow and trim, which is the lightest way into the fabric. The Dries Van Noten Duska Cow-Printed Silk-Velvet Midi Dress is the conversation piece, and the Sergio Hudson Pleated Lame and Stretch-Velvet Midi Dress pairs a gold lamé bodice with a black velvet skirt.

What I would skip: a heavy necklace or scarf with a velvet neckline, and a bag with a rough, snagging finish. Velvet shows every mark. Keep the jewelry small and the shoes smooth.

The Spruce advises steaming delicate fabrics like silk, chiffon and velvet from the underside, inside out, to prevent watermarks, streaking and crushing. Hang the dress in a steamy bathroom the night before, and do not press an iron straight onto the pile.

Here is how I would choose. Start with the invitation, not the dress. Look at the time of day and the venue, and read the dress code as it is written. When in doubt, ask the couple, not a stranger on the internet.

Then pick the fabric for the room. Silk and satin for a formal evening, a long sleeve gown if the venue is drafty, velvet when you want depth of color. Vogue says to stay with jewel tones and rich fabrics for shorter dresses and to avoid anything too light or pastel, and I find that easy to live with.

Finally, test the dress in motion. Sit, reach, hug someone and climb a flight of stairs. If it passes all four, you are done. Pack flat shoes for later, one small bag and a steamer, and go enjoy the cake. If you want to keep browsing, I also put together Wedding Guest Dresses and Fall Wedding Guest Outfits, From Velvet to Plaid.

For the next invitation on your calendar.

Orange Dress

Cocktail Dress Edit

Brown Wedding Guest Dress

Burgundy Dress

Red Dress

Black Lace Dress

Gold Dress

Fringe Dress