Editing Tip of the Day: Real Self-Talk

I looked in the mirror and practiced flipping my long, blond hair over my shoulder. My blue eyes had a sea-green tint to them today--a side effect of my favorite chocolate brown sweater. When I smiled, my rose-tinted lips formed a perfect Cupid's bow.

You've probably read a passage like this before. Describing a character with a visual trick like this is tempting. For one thing, it's easy. Hopefully you can see from the (overdone) example above how false that description reads to the audience.
Generally, you want to avoid the "mirror" cliche, or anything similar, as an easy out to describe your characters. That means no mirrors, still ponds, metallic surfaces, twins, photographs, etc. But the fact that the mirror is an overused cliche isn't the only reason to skip the looking glass. The bigger problem is that it isn't authentic.
Your characters' internal dialogue needs to be realistic, just like regular dialogue.
When a character looks at themselves in the mirror and describes themselves through inner dialogue, we're riding inside their thoughts. And I don't know many people who look in the mirror and catalog their traits like this. I might think, "Wow, my hair looks good today!" But I'm not going to think, "Wow, my straight blond hair looks really good!" because I already know what my hair looks like.
(And please, if you're writing about a character who is a different ethnicity than you, don't use the mirror as an opportunity to point that out. A Black person doesn't look in the mirror and think about how dark their skin is; a Chinese person doesn't look in the mirror and think about the shape of their eyes. Because those are parts of their everyday reality.)
So, while you try to avoid cliched situations like the mirror, think about what's underneath. Dig into what your character really sounds like and how they think of themselves, and then spread the details out to develop your characters more naturally.