Never mind = don’t worry, forget it…
«Mum I failed my exam».
» Never mind, you can try again.»

On my mind = something you are worried about…
«The exam has been on my mind.»

Out of my mind = worried, drugged…
«I’ve been out of my mind with worry over the exam.»

Never you mind = for someone else to forget, not worry about something.
» Mum, why did uncle Carlos touch your bottom?»

«Never you mind,» says mum.

To describe personality…
Narrow minded
Broad minded
Open minded
Closed minded