Many novice writers tend to have a very good idea of what their characters look like, and since they have spent all that time lovingly inventing the character, they feel they need to describe everything, and end up with character descriptions that sound uncannily like a police profile combined with a laundry list.
Example of what not to do:
I clenched my sword tighter and turned to face this new threat. It was a warrior woman of the Tarkety tribe. Her eyes were black, and her skin was the color of warm chocolate. Elaborate tattoos covered her face, blue black swirls under her eyes, and angular triangles across her cheeks. Between her brows was a circle and within it overlapping squares forming an eight-pointed star shape. Her curly black hair was braided along her head with yellow and red ribbons, and were held at the back of her head by a clasp of ivory and coral, and hung down in wavy ebony curls halfway down her back. Her only armor was a hide tunic painted in stripes of grape, grass-green and magenta. It was knee-length with slits front and back to allow her free movement. Below it her sandals were laced all the way up to the knee, and ivory, coral and copper charms dangled from the lacings. More charms hung from her belt of large amber beads, as did the scabbard of her curved silver-hilted sword, that even now she was swinging at my head.
The problem? The description is far too static, and even if we don't fall asleep reading it, by the time we get to the end of the description our warrior woman has had plenty of time to carve our protagonist to mincemeat while he cataloged the color of her beads and the shapes of her tattoos. Also the very denseness of the visual information tends to make it hard to absorb. Quick quiz: 'What color was the warrior woman's hair clasp?' You can peek if you want, because by doing so you prove my point. It's practically impossible for most readers to keep in that many different colors in mind when they are all dumped out at once.
The reader doesn't need to know every detail.
If you want people to know exactly how your character looks, include an illustration. Text isn't the place for it, it takes too long, bogs down the pacing, and the reader won't remember anyway. Besides for many readers part of the fun of a book is that it requires a certain amount of imagination to enjoy, and by describing everything you short-circuit one of the creative joys of reading. Your goal as a writer is usually to convey a general impression, plus a few telling details that will establish that character as an individual.
I clenched my sword tighter and turned to face this new threat. A dark-skinned Tarkety warrior woman swung a curved blade at my head, and I ducked and thrust my own blade at her tattooed face. Her garishly striped tunic covered her from neck to knees, so I aimed my next blow at her sandaled feet.
Try to only describe the things that are relevant.
In the middle of a fight, skin the color of chocolate and the details of what they are wearing are unlikely to be of interest to your protagonist, nor to your reader. Mention details that will effect the flow of action. Wait to note other details if and when they have some significance.
Even if you are NOT in the middle of a battle, a straight forward catalog of traits and belongings is just plain boring. Most readers will be more interested in a description that has emotional impact, or that conveys more information than the purely visual.
Now that she was unconscious I could take the time to study her tattoos. The forehead mark was two squares overlapping to form an eight pointed star -- the symbol of the goddess cult. Even worse she had ivory, coral and copper charms dangling from her belt and from her sandal lacings. I didn't know what they were all supposed to do, but the sheer number of them told me that she was either a shaman herself, or she was near and dear to one. I gnawed uneasily on my thumbnail. It seemed that either the goddess or the shamans must wanted me dead -- or maybe both -- and I couldn't think of anything I had done to anger either faction...
Add movement, use strong verbs.
In my first example the word 'was' appeared over and over and over again. The skin was the color of chocolate, the hair was black. 'Was' and 'is' are perfectly good words, but too many of them gets boring very quickly and using them slows down your text, because they carry no information beyond a state and time of existence. Most things in the world do more than just exist, so when writing descriptions use descriptive verbs to convey movement, shape and mood.
I blinked, having trouble grasping that the Tarkety shaman now wanted me to marry the woman who had tried to kill me just yesterday. I looked at her again, trying to absorb the reality of it all. Her chocolate skin glowed in the firelight, and copper highlights lit the mass of black curls that flowed down her back. She noted me looking at her, and spun about to glare at me, her eyes scornful, and her hands tense. She needn't have feared, my people didn't use tattoos, and I had no interest in a woman with blue black sigals looping and curling under her eyes, and a maze of angular triangles across her cheeks. Besides, her clothing gave me a headache: the colors of her brightly striped tunic warred with the ribbons in her hair who were themselves fighting with the copper, coral and ivory of her many shamanic charms. Neither had I forgotten the curving blade that she had wielded with feline grace and admirable skill; I had no interested in this marriage. Unfortunately, I had no idea how to tell her father that without offending him.
Contrast and compare
Most readers have a selection of mental character 'types' already in their heads. A fast way to create an impression of character can be to invoke a type, and then only explain the unique aspects of this particular character. 'He was a pencil-necked geek, with a vice-like grip, and I looked down at his hands with surprise, wondering how they had gotten so strong. Did he play an instrument?' Although this doesn't actually describe what the character looks like at all, most readers will plug in their own personal picture of a pencil-necked geek, and will be just as happy as if you had actually detailed the short stature, the slight build, the stooped stance, the glasses, and so on.
The danger of this is that when a story is told in the voice of a particular character you can only use types that character is also aware of, although you can invoke types in a more subtle way. If you describe, for example, a 'dark-skinned' woman, your readers will take it mostly for granted that she also has black hair and black or brown eyes. Because on earth the genetic groupings that have the darkest skin also have dark hair and eyes. If you describe a 'tanned' woman, then most readers will picture someone a little more Caucasian looking.
Another way to contrast and compare that works no matter how foreign the narrative voice, or the mindset of the reader, is to compare and contrast one character with another one. If you describe two characters at once then everything you say counts twice. If you compare to someone to a previously introduced character, you can reinforce the earlier character and create resonances between certain characters, because when you use this technique you link the two characters together in a readers mind.
Another Tarkety woman approached me, her mother perhaps? She was older -- thicker bodied, and with a frosting of gray in her braids. But she had the same proud tilt to her chin, the same striking color sense, and an equal plethora of charms dangling from her person. She didn't have the goddess mark. That surprised me -- weren't members of the goddess cult usually initiated by their mothers?
A Final hint:
I am working on a story that takes place in an imperial court. Several of the characters are introduced by a rather complete and detailed description of their clothing, because in that setting fashion is relevant. (Faces are described vaguely if at all.) Ignore any of the above hints, if they don't fit your story. But remember: although my readers did not protest the descriptions, because they 'fit', and were necessary to creating the right feel, that didn't mean they read all the sartorial details, either. When you must describe in an over-wrought way, you might want to consider putting the most important details first. That way if the last half of the description is skipped, it won't have a negative impact on the reader's enjoyment of the rest of the story.