This concept is so simple and genius , and really common sense if you think about it, that I wanted to share it :
Play something : Observe what your mind first think about. Write down that first thought. That thought is a barrier for feeling the music, and needs to be removed (if your goal is to express yourself freely). Isolate that one thing, solve it, and move on.
The awesome stuff about this is that you know what to practice (the first thought), and what order ( first thought is what you need to remove first )
Example : You improvise. The first thought you come up with is " the playing is sloppy, the notes are covered by noise". Then you know what to sit down and isolate.
This is the key masters do consciously or unconsciously.