Dialogue and reflection are my go-to. Comparison is another common one.
Really, though, you have to consider how a character looks in relation to its importance. What's significant? In current MS, being biracial is significant to my MC; in previous MS, being the wrong colour was again signficant. If your character is caucasian and not especially old or young (say, 20s to 30s) and their appearance doesn't figure into the story or themes, leave it out if you want.
So--some ways I've put in appearance for current MS. These are scattered all throughout the MS. But the general idea is to throw in enough for the reader to latch on to, and build up a gradual picture.
I'm not saying it's good and some will DEFINITELY find it clunky, but even if you dislike that as an approach that's worth a comparison. The first one is the most gratuitous and forced.
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Everyone else has someone to sit with, or text, or talk to; everyone else has somewhere to go, places to be. In the network of life the other passengers are connected in a maze of invisible lines. Remy, though, is a broken thread; cut off from the rest and only masquerading as part of the weave.
She wonders if they see through her facade, if they see her at all. Behind the glasses, uneven brown bangs, and hoodie zipped up to her chin, there’s not a lot of face left to find. Dark eyes, darkish skin; both a muddle of her mixed-up ancestry. A blur of mediocrity, wrapped in cheap clothing. But even if she gets contacts, buys makeup, and wears better clothes, not much will change. More accessories will just render her into the Invisible Man—a detritus of items hanging off an aerial spectre, features nonexistent beneath.
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Remy lounges on the balcony. Sunbathes in the remains of the day, not that she needs to be any darker.
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“Hey,” he says, wiping himself down on her pillow. “Where you from, baby?”
“Montana. Like the song.” No one ever knows the song she means.
“Naw, I mean originally.”
“Originally, Montana.”
“Huh. You look kinda paki, or something.”
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“Hey, so, mind if I make some changes?” I’m already reaching for the scissors in her medicine cabinet.
"Um. What kind of changes?”
“Your hair, for starters. You look like goddamn Velma from Scooby Doo, except browner. Not cool, Remy.”
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Aisling is crunched up next to her, as if clinging to some invisible surface. Shorter than Remy, and Remy isn’t tall. Older than Remy, by ten or fifteen years at least. Maybe more; maybe twenty. Pretty, in a faded way—grey eyes tired, blond hair greying. Dressed in white pajamas.