Hyphen

Use hyphens for compound words:

例: a five-minute walk; a high-speed chase; the front-right seat; a never-seen-before magic trick; the blue-white train; a flow-type air micrometer; etc.

Use hyphens for numbers:

例: a thirty-three thousand dollar car; sixty-two billion dollars in tax cuts; eighty-four yen per dollar; two-tenths of a percentage point

Use hyphens with some prefixes:

例: anti-aging cream; extra-condensed; semi-independent; self-help therapy; half-baked idea

Note:

Be sure to check a dictionary for proper spelling. Some compound words have become single words. For example, the term "electronic mail" became "E-mail" with a hyphen. Then, "E-mail" became "e-mail" with a lowercase "E." Then, "e-mail" became "email" as one word.

References:

1. APS Style Manual (http://www.apsstylemanual.org/apsHouseStyle/punctuation/hyphens.htm)
2. The Mayfield Handbook of Technical & Scientific Writing at MIT (http://www.mit.edu/course/21/21.guide/hyphen.htm)
3. The Chicago Manual of Style, 15th Edition