Start with
JAR 66, JAR 145 and JAR 147. Also
EASA Maintenace.
For reference / training material see:-
CAA Human Factors Publications.
CAP 715 An Introduction to Aircraft Maintenance Engineering Human Factors for JAR 66.
CAP 716 Aviation Maintenance Human Factors.
CAP 718 Human Factors in Aircraft Maintenance and Inspection.
CAP 719 Fundamental Human Factors Concepts.