When I began my research into the correct use of hyphens, I stumbled across a sentence that said hyphen use is among the least uniform and least stable feature of English spelling and to consult a dictionary. Being that I have latent masochistic tendencies, I did not give up.
But you’ve been warned, this could very well be a waste of your time. I will, of course, have learned something–even if it is wrong–so I will have accomplished something.:D

Hyphens are used for:
1) Compund words–not all, and I guess this is where a current dictionary will come in handy.

Correct: Able-bodied, bull’s-eye, six-pack abs, in-laws, one-sided, Governor-elect
Incorrrect: Bridesmaid, stepfather, highlight, headquarters, bittersweet

2) Compound numbers from twenty-one to ninety-nine. Fractions may or may not be hyphenated.

Example: One-third of the students dropped the class.
Example: One-third are illiterate.

3) Some prefixes require a hyphen.
Like all-, ex-, quasi-, self-, and sometimes co-
On prefixes before words that begin with a capital letter: anti-Ameican, pan-Pacific
To prevent the joining of two identical vowels or three identical consonanats: semi-independent, fall-like.

4) With group modifiers
Example: Growing up I always watched the after-school specials.

Note: this doesn’t apply if there is an -ly adverb modifying the noun.

Now that I’ve finished, I think I’ve done this before. Hmm, guess it doesn’t hurt to get a refresher. By George, I think my brain is getting it.