Criminal trial lawyering is a subcategory of trial lawyering, which is a subcategory of persuasion, whihc is a subcategory of communication.
So the criminal trial lawyer, to be better at her craft, could study the lessons of other trial lawyers (personal-injury lawyers, for example). That’s obvious. The good thing about personal-injury lawyers is that they are fighting over money. ((It’s also the bad thing about them.)) Because they are fighting over money they have money to spend on investigations into being better trial lawyers. Few are motivated to do so, but those that are, are also financially able.
Less obviously, the criminal trial lawyer, to be better at her craft, could study other persuaders, such as salesmen, and preachers, and politicians and other conmen. Salesmen write ad nauseum about how to be better salesman—How to Win Friends and Influence People is a classic manual of persuasion. I don’t know that preachers write about their craft, but they can be watched in action. The art of the con is more opaque, but no less worthy of study.
Still less obviously, the criminal trial lawyer who wanted to improve could study the crafts of other communicators , such as teachers, and actors, and writers, and probably musicians and dancers. Anyone who has given serious thought to how to make people feel or understand things will have a lesson for the criminal trial lawyer, if the lawyer is willing to listen.