The Inner Game of Tennis (1974) by W Timothy Gallway is a well written, insightful book on how to improve almost any activity.
Gallway posits the abstraction that there is an unconscious self, self 2 that performs physical actions while there is a conscious self, self 1 that is verbal and tells self 2 what to do and very often does more harm than good. Self 1 often makes self 2 tense up, focus on the wrong things and causes mistakes by being under confident or over confident.
Gallway describes how to quieten self 1 and observe self 2 and let self 2 work on improving and being as good as possible. He emphasises that focus and being in the zone are what really improve performance.
The book is simplistic, but it has a valuable lesson. Focus and try and observe but not criticise what you are doing and then improve. The book perhaps neglects the role of practice, but definitely makes good points. It’s also applicable to more than tennis. It’s a short and interesting read.