Directing is fun. The only way to learmn to be a director is To watch other directors in their work. As a result every directorial technique is different, and so there are few, useful, books on the actual mathodology involved, but more on the process of organising a performance. Directorial technique should not be confused with practicioner thory, which deals with the role of theatre and elements involved.
In conclusion it is pointless to write about directing because it depends upon the personal approach of each person to a performance text.