I received a link to this delightful (albeit accurate) list of typographic sins from Laura Caldwell via Abraham Piper’s 22 words blog. Thank you to both. Following is an excerpt, but you can find the full original 34 sins here.

Ten

Typographic Sins

1. Two spaces between sentences.
   Repent of this sin by using only one space.
2. Dumb quotes instead of smart quotes.
   Evil: "Thou shalt not misuse type"
   Good: “Thou shalt not misuse type”
3. Dumb apostrophe instead of a smart apostrophe.
   Profane: Don't use prime marks
   Sacred: Don’t use prime marks
   By the way, apostrophes always face this way: Pot o’ gold.
   They never face this way: Pot ‘o gold.
4. Failing to tuck punctuation inside quotes.
   Immoral: “I love type so much”, she confessed.
   Chaste: “I love type so much,” she confessed.
5. Failing to kern display type.
   Unseemly gaps can impede readability and be distracting to the reader. Adjusting the spacing between letters will assuage your guilt.
6. Using a hyphen instead of an en dash.
   Use an en dash to indicate a duration of time instead of the word “to”:
   the 8–10 commandments, not 8-10 commandments.
7. Using two hphens instead of an em dash.
   An em dash signifies a change in thought—or a parenthetical phrase—within a sentence.
8. Too many consecutive hyphens.
   It is sinfult to have more than two hyphens on consecutive lines of type, and even that should be avoided.
9. Large amounts of bodytext in uppercase letters.
   IT BECOMES REALLY DIFFICULT TO READ.
10. Large amounts of reversed type
      ARE HARDER TO READ.   Type on a busy background is also unreadable.