How do you train that? How to you structure your training, both body and mind, to have the body stable as much as possible no matter the circumstances? No matter which side of the equation it is operating on......
Simply by training, that's what training is for is it not.
Body stability firstly comes through kata, drills of motions, practice until the body is used to the moves and comfortable with them. Thus the first level of body stability.
This is repeated and true for various levels when new motions are introduced.
Mind is a matter of practice and drills too with the focus on it, thus leading to stable mind.
When the physical motion is comfortable and the mind is too you have mind and body coordination.