Dashes, when used sparingly and correctly, can be used to make your writing sound more sophisticated.
Indicate sudden changes in tone or thought within a sentence
To emphasize the contradiction between ideas
There is an illness in many foreign services--the people in them are only good at following instructions.*
I am under the impression that she has no instructions at all--and doesn't need any.*
The exuberant--I should say lunatic--quality of his ravings electrified the crowd. *
Set off some sentence elements
To insert parenthetical commentary while emphasizing their importance (Parentheses tend to diminish the importance of what's enclosed in them)
Over a candlelit dinner last month at Spaso House, the ambassadorial residence in Moscow, Robert Strauss and his wife Helen listened as two Senators--Republican Robert C. Smith of New Hampshire and Democrat John Kerry of Massachusetts--agreed that the way to bring American audiences "out of their chairs" these days was simply to say, in Smith's words, "We won the cold war, and we're not going to send one dime in aid to Russia."*
Strauss favors--as does, sotto voce, the Administration--early admission of Russia to the International Monetary Fund.*
To connect ideas strongly to each other.
To feed, clothe, and find shelter for the needy--these are real achievements.
For further information you may wish to take one of the following free grammar, style, and punctuation workshops offered by the Writing Center.
*Adapted from Time Magazine, 6 April 1992.