Follow the guidelines in the Chicago Manual. (The manual’s hyphenation table includes examples of most uses of hyphens.
A few general guidelines include:
- Nationality combinations: ethnicity combinations should be written without a hyphen even when used as used as an adjective. African American history, Latin American culture
- Numbers: from twenty-one to ninety-nine, when spelled out, are hyphenated.
- Fractions: hyphenate a fraction when it is used as an adjective (e.g., a two-thirds majority). Write as two words when used as a noun (e.g. two thirds of the participants).
- X-to-Y combinations: 16-to-32-year-olds
- Invented verbs: Woods three-putted on the ninth green.
- Suspended hyphens: They climbed the third- and fourth-highest peaks.
- Prefixes are generally solid. Follow entries for individual words as indicated in Merriam-Webster’s Collegiate Dictionary.