To hyphenate or not to hyphenate — that is the question. A general rule is that if the words in question go with (usually before) a noun, hyphenate. If they go with (usually after) a verb, do not.

They had a face-to-face meeting. They met face to face.
He has a full-time job. He works full time.

Adjective-noun combinations that modify other nouns should also be hyphenated to avoid confusion: Small-business owner, criminal-court judge. We don’t want to call the business owner’s stature or the judge’s morals into question!