Hyphens join words together and should be used to help form a single idea from two words or avoid ambiguity in your writing.

While the AP Stylebook admits that there is not necessarily a standard way to use them, and that most instances come own to personal style or taste, it does say the fewer hyphens the better.

Avoid ambiguity: Use a hyphen whenever your sentence’s meaning would be ambiguous without it: “The mayor will speak to small-business women.” “Businesswomen” usually is one word, but “The mayor will speak to small businesswomen” is not clear.

Compound modifiers: Use a hyphen if a compound modifier precedes a noun, except with the adverb “very” or for adverbs that end in “-ly”: “a first-place medal,” “a part-time job,” “a very dangerous journey,” “an easily forgotten law.” Such combinations are generally not hyphenated if they occur after a noun.

• When a modifier that would be hyphenated before a noun occurs after the noun, but in a form of the verb “to be,” the hyphen must be retained in order to avoid any confusion: “The woman is well-known.” “The child is quick-witted.”

Two-thought compounds: “serio-comic,” “socio-economic.”

Prefixes and suffixes: Though many of the most commonly used prefixes and suffixes have their own AP Stylebook entries, but a few general rules hold true when it comes to hyphenation.

• You generally don’t hyphenate when using a prefix with a word that starts with a consonant.
  Three consistent rules:
  –Except for “cooperate” and “coordinate,” use a hyphen if the prefix ends in a vowel and the word that follows begins with the same vowel.
  –Use a hyphen if the word that follows is capitalized.
  –Use a hyphen to join doubled prefixes: “sub-subparagraph.”
• For suffixes, if a word combination is not listed in Webster’s New World College Dictionary, use two words for the verb form; hyphenate any noun or adjective forms.

Avoid duplicated vowels, triple consonants: “anti-intellectual,” “pre-empt,” “shell-like.”

With numerals: Use a hyphen to separate figures in odds, ratios, scores, some fractions and some vote tabulations.

• For large numbers that must be spelled out, use a hyphen to connect a word ending in “-y” to another word: “twenty-two,” “fifty-eight.”