Relevant books

for ISCA you can either go for Dinesh Madan's book or you can take Munish Valecha's book.

Madan Sir's book is popular for its Simple language.

But i personally prefer Valecha's book, it have Lots of Mnemonics you can learn ISCA with them easily.

for IDT i dont know very good book out in the market for self study. Although you may go for Deepak Gupta Sir or Raj Kumar Sir.

Best Study Material

ISCA: Dinesh Madan Book

IDT: Bangar Sir Book