Vaibhav is Right, for ISCA you should refer the Study matrial issued by the Institute, dont forget to refer Practise manual given by institute. this will help you to understand the papers pattern and what type of qwality answer we have to right in exam.
For costing use paduka.. Lay deep emphasis on operational research must do theory in cost..
For dt vg sir book is enough
Idt dg sir lay emphasis on practical questions see practise manual..
For isca just pick up study n grasp all the headings and understand the inner matter.. I scored 58 in isca...
Best f luck...