If you like dashes, you may be tempted to use them too often. Dashes are more noticeable than commas. So remember a basic rule: Don't let a punctuation mark become a distraction.
When you type, don't confuse a dash with a hyphen. The hyphen is mainly used to break syllables of a word: pre‐existing. A short dash (en dash –) is used with ranges ( April 1–5, pages 70–75). A longer dash (em dash —) is typed as two hyphens with no space between them. Most word processing programs convert the two hyphens to a longer dash (see the following examples).
Ms. Persinger‐‐ the most important official in the city‐‐okayed the plan.
OR Ms. Persinger— the most important official in the city—okayed the plan. (better)
NOT Ms. Persinger‐ the most important official in the city‐okayed the plan.