This excellent publication from Jeppesen's Guided Flight Discovery team, covers all the information needed to becaome a proficient IFR pilot including instruments, ATC, charts, approaches, weather etc.
THIS BOOK IS FOR AERO PLANE PILOTS who already hold an ICAO IR, and who can simply convert to the EASA version by
completing the skill test and demonstrating during the skill test an adequate knowledge of air law,
meteorology and flight planning
The Instrument Flying Handbook is the primary FAA source for the Knowledge Exams that cover the IFR system as well as aerodynamics, flight instrumentation, attitude flying and navigation as they apply to the instrument pilot.
Instrument Procedures Handbook explains to instrument-rated pilots how best to use the system they've been trained for. The FAA's Instrument Procedures Handbook is a great resource for instrument-rated pilots!
The Practical Test Standards is a guide for students, instructors, and FAA-designated examiners to know what is expected of pilots during Instrument Rating (Airplane, Helicopter & Powered Lift) checkride.