Personal Development is probably the most practiced discipline amongst successful people!!! You have to be in a constant state of growth in order for you to live up to your highest potential! Whether I am trying to be a better mom, leader, wife, friend, good with my finances, etc I am always trying to better myself.
My favorite personal developement books or audio are:

The Slight Edge

Eat That Frog

The 5 Love Languages of Children

Goals

Crush It

The Mentor Leader

The Compound Effect

Chalene Johnson’s – Carsmarts