When you have an adverb ending in ly, followed by a participle or an adjective, do not hyphenate it, whether you are using it before or after a noun.
a highly paid banker
he was mildly amusing
For adverbs not ending in ly + participle or adjective, use a hyphen before a noun, but not after.
a much-needed addition
this addition was much needed.
the best-known author
He is best known for his research on migratory birds.
Compounds with more, most, less, least, very are generally open, unless ambiguity becomes an issue.
Most skilled workers had to also sit for a language proficiency test. [most in number, hence not hyphenated]
The most-skilled workers were recruited on a full-time basis. [most in skill, so hyphenated before noun (workers)]