At some point in your story, you'll have to decide how much to include about the physical description of a character. You don't want to describe your characters to death, but you also want to describe them so readers can get an idea of what they look like. How much is too much and how little is too little?
This is one of those things that's really up to the author. I dislike a lot of description, and I admit, I skim a passage when it's clear it's a big "this is what stuff looks like" paragraph. Even description about a character. I'm much more interested in who they are and what they'll do than what they look like.
Because of my personal feelings, I tend to be sparse when I write my own character descriptions. In fact, if I didn't know there are folks out there who love knowing what someone looks like, I'd probably skip them altogether.
But that's just me, and my way may not be your way. So, quick answers:
How much is too much?
If it bogs down the story, it's too much.
How much it too little?
If there's no sense of who the person is, it's too little.
How important is it to describe them?
Some authors never do. If it's important to you, do it. If not, don't.
I think any description, be it about a character or a place, has the potential to bog down a story because description stops the action. So we need to be careful about how we slip it in and how much we use.
My own rule of thumb is, the more details you add, the more you need to keep it in your point of view (POV). Let them judge what they're seeing so the details do more than just describe. They also characterize and do some world building at the same time.
The man was tall, six feet six inches, with broad shoulders. He had short blond hair and brown eyes, and wore a olive green double-breasted suit.
This, I'd skim. It tells me details, but so what? Unless this is the exact description of the killer, it does nothing to move the story along.This tells me nothing about who this guy is or who the person looking at him is.
Try the same details in a solid POV.
He was tall, like, basketball tall, with shoulders wide enough to block any jump shot. But no star athlete would wear that haircut, even a blond one. His brown eyes sparkled with more intelligence that you'd think at first glance, as if he knew what he looked like in that too-fancy-for-just-lunch olive suit. And come on, double breasted? In this neighborhood? Please.
Here we learn just as much about who the POV is as we do what the guy looks like. The POV knows sports, or at least basketball, they don't think too highly of folks who are dressed a certain way in that area, suggesting some type of prejudice. This is a person who sees things and immediately judges them. But they're also perceptive, since they noticed the subtleties of the eye sparkle.
(More on describing your first-person protagonist here)
You don't have to flesh it out as long as this, though. You can sum up a quick description in a way that still feels like your POV.
The man stood out. Six foot six, olive suit, blond hair, brown eyes, broad shoulders. He was worth keeping an eye on.
Much shorter, and with a tone that suggests whoever is keeping an eye on him might have some police or military background. The details are taken in quickly, but what comes before and after those details is judgment about them. That's turns this from bland to interesting.
Of course, you can also describe without giving away too many details.
He was the kind of guy who belonged on the cover of a romance novel.
I didn't give one detail of actual description, but I bet every one of you pictured something specific. Very likely the broad-chested, well-muscled guy with long flowing hair, either blond or black. (Fabio, anyone?) This image has become a cliche, and you can use that cultural knowledge to fill in the blanks.
(More on making the most of your descriptions here)
When describing characters, you don't have to put in more (or less) than you feel the story needs. What's more important is what those details bring to the page than what they are.
How much do you describe? Do you like knowing what a character looking like? Why or why not?