If the key signature has no sharps or flats, the piece is in C major (or A
•If the key signature has one flat, the piece is in F major (or D minor).
•If the key signature has more than one flat, the piece is written in the key of
the next-to-last flat in the key signature.
•If the key signature has sharps, take the note of the last sharp and go up
one note (changing the letter name). If the last sharp is D sharp, the key isE. If it’s F sharp, the key is G.
•The relative minor of a key is a minor third down from the major. So when
you move three adjacent keys, black or white, to the left — or three frets up the guitar neck (toward the tuning pegs) — you land on the relative minor.