Well the best way to describe someone in fiction is to do very little direct description at all but build up a picture from other people's comments and thoughts and their actions.
For example 'She had long brown hair' is a bit dull and brings the reader out of the story with a bump. Telling us
'As she passed the mirror she paused to check her hair. "God it needs a cut" she thought, turning to peer down her back at the ends. "not only split ends, but the bottom is a completely different kind of brown to the top where it's grown out so much. I'll make an appointment tommorrow.'
This not only tells us she has long brown hair, but that she hasn't been taking care of it...but she seems to care about its appearance...perhaps she has been short of money....but she can go to the hairdresser now....I wonder why......hmmmm...a bit of insight into her life.