In the opinion of this old fart, is to get a copy of "In Gravest Extreme' by Massad F. Ayoob.
I first read this book about 30 years ago, and have used it for training since then. Mas is the best trainer I have ever met, and I have trained with many of the 'old masters'.
In Gravest Extreme, is not a 'how to book'. Rather it is a when to, and when not to, and a consequences book.
Go slow and stay safe out there