Use a hyphen when you join two words to form an adjective. This eliminates confusion.
Use no hyphen when the meaning is clear and there is no ambiguity.
Never use a hyphen where an "ly" adverb modifies an adjective:
A hyphen should not be used to join a prefix to a root/base except to avoid doubling a vowel, tripling a consonant, duplicating a prefix or when the context is confusing or causes ambiguity.
Use a hyphen with the prefix "re" where the word would otherwise be confusing.