Insert hyphens between words you combine to form an adjective. Dashes are used to separate information, usually because you want to stress it.
We use hyphens in a few instances, but mostly common, you should use them to join two or three words that are serving as one modifier, describing an adjacent noun, as in “cost-saving tips” and “next-to-last meeting.” There is room for discretion; if you see no risk of confusion, you can omit it. For example, some people will hyphenate business-writing course, but many people will not, and in that case, you can get by without it. Sometimes, as readers of English, we are accustomed to seeing certain words adjacent to each other (such as business writing), so the lack of a hyphen would not impede the reader’s forward motion.
Readers can be confused on other occasions, however. On the surface, the sentence “He is our new media strategist” means that you have a media strategist who is new to the company. But the writer’s intended meaning was that the strategist had expertise in the field of new media, so it should be written that “He is our new-media strategist.” When you do not put in hyphens, each word modifies the noun individually, so the meaning is that he is a media strategist and he is a new strategist.
Similarly, without hyphens, the phrase “toxic gas detector” refers to a gas detector that is toxic, which obviously is not the intended meaning. It is a detector that identifies toxic gas.
Caution: Don’t get hyphen happy. If you over-hyphenate, it creates boring reading. Use judgment. Use them often, but there are occasions when they are not necessary and in come cases would look awkward if you put them in.
One final note: We do not hyphenate words ending in “ly” because no confusion ever seems to result from the word combination in such phrases as “freshly prepared food” or “carefully written proposal.”
