When we’re describing characters, particularly if we’re writing a first-person/subjective narrator or a limited third-person/limited omniscient narrative voice, that one character’s view of another will be biased. It’s unlikely two characters will agree on what’s attractive, one person’s idea of size is different from another’s, and there’s one character’s emotional connection to another affects how they describe them.
Perhaps the most conspicuous example of biased is the notion that all romantic lead characters are handsome/beautiful. They might be or they might not be but they will be to each other, it’s a romance story there’s bound to be an attractiveness biased in the description of the love interest. If we use an arc where they two characters do not begin and love interests then we can show their changing feelings through the way they describe each other. We can even flip expectations and show they don’t fit the cliché while showing they’re attractive to each other.
Simply because love interests have an attractiveness bias towards each other doesn’t necessarily mean that villains have to be described as ‘unattractive’. We can dislike people but still appreciate their attractive qualities, or indeed dislike them because they’re attractive. When we’re describing our characters ‘attractiveness’ should not be at the fore but rather what they look like and why they look like that. For instance, someone may look pale because they’re ill, muscular because they do a lot of heavy work, or wear their hair short because they don’t like it long (see related article here). We don’t have to tell people all these things but it can help to consider them because it can help us learn more about our characters.
It’s also important to remember that when characters describe themselves they also have a bias, there may be something about themselves they don’t like, something they do, and reasons they wear what they do. Once again we don’t have to have all of this on the page but there may be moments we can build these things in, even if it’s something as simple as someone criticising a haircut and our character touches their own hair. These details can make our characters more vivid and alive for our readers because they’re relatable observations. It’s common for some to, perhaps, dislike the colour of their hair and then have someone else tell them it’s lovely or do something that in their mind confirms there’s something ‘wrong’ with their hair. Characters need these kinds of worries as real people do to give them depth.
However we choose to describe our characters we have to bear in mind these potential biases because they inform readers as much about the characters doing the describing as they do about the characters being described.