Most stories have what literary scientists call characters; fictional people who the reader chooses to believe are real. Or the reader chooses to believe this if you manage to make those characters at least halfway believable as people and at least 56% interesting.
A lot of writers think the first part (believability) is hard and the second part (interesting) is easy. After all, making characters pop off the page can be accomplished in a variety of ways, from a distinctive accent or catch-phrase-laden dialog to costuming, physical appearance, and perhaps really crazy hair. You can almost tell you’re reading a pretty awful story simply by stepping back to observe the characters, because there’s an inverse relationship between the quality of the story and what the characters are wearing.
It boils down to: The crazier you make a character’s defining characteristics, the less believable they are. Because if a man walks into a room wearing a cape, with a parrot on his shoulder, no one thinks look at this fascinating man! They think, who in the world wears a cape? and they pop out of your story as if shot out of a cannon.
Unless, of course, you’re writing a story set in a place where capes are common, in which case: Carry on, but you get my point.
People Be Crazy
In real life, people who dress outrageously aren’t the cool characters of your story, they’re the people you don’t want to sit next to on the subway. Defining your characters by a verbal tic, accent, or strange appearance is easy—guy in a cape, got it—but the cape doesn’t make them a distinct character on the page, it just means your reader can’t think of anything else when they’re doing something.
You’ve got to make your characters distinct the same way people around you make themselves distinct. We all (or most of us) play along with certain conventions of society. We dress within a fairly narrow range of acceptable fashions. We speak certain ways to strangers, slightly differently to friends. Within a spectrum, everyone basically behaves the same way because as George Costanza once said, we’re living in a society here and that’s part of it.
So how do you tell your friends apart if we’re all within this range of normalcy? Their opinions. Their backgrounds. Their way of speaking (which may actually include an accent or catch-phrase, to be fair, though that’s rarely the only thing that distinguishes them). Not using the easy physical markers to define your characters will force you to dig a little deeper and make them into people with motivations, back stories, and subtle traits that make them stand out.
Unless your character is a magician-pirate, in which case go with the cape and the parrot.