1. Find your comfortable lowest and highest notes: sing along to a keyboard and slide up and down until it strains.
  2. Find the song's highest notes — usually in the chorus — and notice how long you stay up there.
  3. Move the song up or down until those notes sit just under your top, on the most emotional words.
  4. Big, intense songs can sit a little higher (a touch of strain sounds passionate); quiet ones a little lower.
  5. Try three keys, sing each, and keep the one where you sound most like yourself.