Dashes, hyphens and brackets

Different lengths, different jobs.

Hyphens

A hyphen joins words into a single modifier: a well-known problem, a five-year plan. It removes ambiguity rather than adding decoration.

No hyphen after an -ly adverb: a badly written report.
Compound modifiers before a noun usually take one; after the noun they usually do not.

Dashes set off an aside emphatically; brackets do it quietly. Both should be occasional, or the sentence stops having a main line to follow.