Elmore Leonard had 10 rules for good writing. #8 was avoid detailed descriptions of characters. That seems odd, doesn’t it? Shouldn’t you try to paint a picture for the reader?
There are a few considerations here. First, the preference nowadays is to leave most of the description up to the imagination of the reader. Describe what matter. If a character has a limp and the protagonist will later identify him in the dark by the sound of his gait, it’s a significant item of his appearance. If the limp was caused by an explosion when he was a soldier, it’s a significant link to the person’s history or character (i.e. that he was patriotic enough to enlist.)
Usually, the only details worth mentioning are those that do double duty: they don’t just describe, they either reveal depths of character or will be essential to the plot.
Inexperienced writers often add throwaway details. A man with brown eyes held the door open for her. If we never see the guy again in the story, who cares if his eyes were brown or blue?
Second, pay attention to who is observing the character. If your protagonist is a detective or a portrait artist, your protagonist would be one who would notice details, like hair color, nose shape, or posture. Most people don’t notice many details, especially at the time in the story that the person appears. If your protagonist is running for his life, the eye color of the person chasing him won't even register.
Third—and this is linked to the last point—pay attention to when your protagonist would notice the character’s appearance. I’m reading Jodi Picoult’s Leaving Time. One character, Alice, an elephant researcher in Africa, is ticked that she has to babysit a tourist coming to see their reserve. The story is in first person. Here’s what she doesn’t say: The man got out of jeep and walked over to me. He had green eyes. She doesn’t say, A green-eyed man got out of the jeep and walked over to me.
No. For several pages there’s some activity, the task of collaring an elephant. Before and after she’s rude to the guy. After he says something that makes her realize that there’s more to him, that his views on elephants match hers, she begins to see him as a kindred spirit. She stares at him. That’s the time we learn that he has green eyes. She notices (and mentions) eye color when what he really is, inside and out, suddenly matters to her.