Do use a hyphen if it’s needed to make the meaning clear and avoid unintended meanings:
better-qualified candidate, little-known song,
(Think of the different possible meanings or confusion if the hyphen is removed in each of those examples.)
Other two-word terms, particularly those used as nouns, have evolved to be commonly recognized as, in effect, one word. No hyphen is needed when such terms are used as modifiers if the meaning is clear and unambiguous without the hyphen.
third grade teacher, chocolate chip cookie, special effects embellishment, climate change report, public land management, real estate transaction, emergency room visit, cat food bowl, parking lot entrance, national security briefing, computer software maker.
Hyphenate well- combinations before a noun, but not after: a well-known judge, but the judge is well known.
Generally, also use a hyphen in modifiers of three or more words: a know-it-all attitude, black-and-white photography, a sink-or-swim moment, a win-at-all-costs approach. Consider carefully, though, before deciding to use more than three modifiers.
No hyphen is needed to link a two-word phrase that includes the adverb very and all adverbs ending in -ly: a very good time, an easily remembered rule.
Many combinations that are hyphenated before a noun are not hyphenated when they occur after a noun: She works full time. She is well aware of the consequences. The children are soft spoken. The play is second rate. The calendar is up to date. (Guidance changed in 2019 to remove the rule that said to hyphenate following a form of the verb to be.)
Often, arguments for or against a hyphen could be made either way. Again, try to judge what is most clear and logical to the average reader. Also, consult Webster’s New World College Dictionary.