At risk of giving away the secret--- when doing song accompaniment
on melodeon, you can just flog away on chords, both ends.

However, you also can take the place of a fiddle, and do so
very easily. The trick to know is that on the 'home' row for
the currently active chord, there is no note that is wrong.

That means you can play nicely around the melody. On the other
hand, the notes on the 'cross' row make the 'passing' tones.

So when choosing a note to 'dwell' on, do it on the 'home' row.
Pass through the other notes.

Everyone will think you a genius, when in fact it is the fellow
who designed the melodeon.