At common grammatical mistake is to use an N dash used instead of M dash (hyphen instead of a dash).

The following uses a hyphen or N dash (one single dash): My mother-in-law

The following uses an M dash, a long dash or two dashes to represent a break, interruption:

 “I was on my way to the—Whoa, what are the neighbors doing? Honey, get the binoculars.”

More useful hyphen usage:

Hyphenate numbers, ages and descriptive words when they become a compound modifier which is often before a noun. There are a lot of exceptions. Below are all correct examples.

The tie is emerald green

The emerald-green tie

She is a twelve-year-old.

She is twelve years old.

Chapter Twenty-one up to Chapter Ninety-nine use hyphens.

http://www.quickanddirtytips.com/education/grammar/hyphens

http://www.chicagomanualofstyle.org/16/images/ch07_tab01.pdf#page=1&zoom=auto,0,576

Correct the Following:

“Don’t tell me what to do. I’m not your submissive, Fifty Shades of Grey bi-”

Maria said, “Hey! I only asked you to try the spank—o–matic.”

Chapter Two-hundred and Seventy two

My half full cup isn’t half-full.

I’ve been twenty-nine-years old for twenty one years.