What is the most important self-improvement skill?

The ability to be truthful to yourself and understand what you are, who you are, why you are as you are, and especially why you do the things that you do.

Being honest with yourself about yourself means that you will truthfully make the right and correct changes to your life that will help you with “Self”-Improvement.
Life success Is Not about recreating Yourself, it Is About Making you a Better You by removing whats not good for you and what is not helping you, such as bad habits, character flaws, weakness (as in morally and so on) and striving to be a well rounded competent, mature adult.
As a competent mature adult you will be well liked, responsible, a good parent, good at what you do to the best of your ability and able to cope when you fail, and able to be mature when you succeed by thanking those who helped you along the way and being thankful for the true, honest and loving people in your life.
Be true to yourself.

All the best from James Martin Sandbrook.
Dec 2022.