I will tell u wat i did. I thoroughly prepared for Operational research part from Institute's practice manual and from guru kripa's AMA book. Its an easy scoring area so don't leave this. For the costing part institute study material, practice manual ( compulsory ) and any book which explains theory well like guru kripa, L. Muralidharan's book is good. I scored 67 in this paper.
THE BEST BOOK FOR SELF STUDY ON ADVANCED MANAGEMENT ACCOUNTING IS WRITTEN BY DR.P.C.TULSIAN AND CA.BHARAT TULSIAN.THE BOOK HAS BEEN WRITTEN IN A VERY SIMPLE LANGUAGE.AND BASED ON SELF STUDY CONCEPTS.THE BOOK HAS BEEN PUBLISHED BY S.CHAND PUBLISHERS.NEW DELHI
Refer padhuka book plus practise manual plus recent RTP. Try to understand the concepts and do solves the probelms wihtout refering solutons and let you commit mistake and correct