One of the easiest ways to improve your future playing in most keys is to re-arrange the chord bars on a 21 chord harp so the same relative position of the 1,IV,V, and relative minor is preserved. There are several ways to do it described at the autoharp.org website. I put the majors in the middle, the 7ths in one row and the minors in another row. It's best to make the change before you get accustomed to the factory arrangement which is not as consistent.

JAB