The point in describing a character is twofold. First, so the reader can have something to look at in the mind’s eye. Second, so the writer can have something to look at in the mind’s eye.
Don’t be so detailed that there is nothing left to the reader’s imagination. Remember, good writing is also the ability to stimulate the reader’s imagination. I read that Margaret Mitchell when visualizing her character Rhett Butler in Gone With the Wind, described Charley Chaplin. However, Hollywood came up with Clark Gable. The fact is, they have similarities, yet room for imagination.
There are no rules or standards for how this is done. However, it suffices to say to only describe enough to make them differ. And it’s not enough to say one was fat and the other skinny.
As a personal preference, I start with hair. Hair is almost like a finger print; between the color, type, length, and styling, seldom are any two alike. Then I focus on facial characteristic, one or two at the most. Normally I leave body build and height alone unless it is important to the story or character. If I’m a short and fat writer, everyone may turn out to be a tall and thin character. Those are things that are normally relative. Kind of like saying for a Pigmy he was tall.
It is not generally a good idea to describe everything about the character in a sentence or two. Stretch it into something that occurs. “Every time Lyle became nervous he ran his stubby fingers over his thin strands of greasy hair.” Much was told about Lyle (besides not wanting to shake his hand) from just a nervous habit.
Develop the character early. I don’t want Lyle’s stature revealed on the last page, especially when I thought all along that piano players had long thin graceful fingers. Indeed some have stubby ones—Billy Joel.
Remember, in describing your character, don’t overdress.