WHICH BOOK IS MOST USEFUL IN GATE WITH AUTHOR FOR EEE?

Basically, you need to focus on your B.Tech syllabus first because Gate is based on that only. Once you get a good grip on your preparation, you need to practice on sample papers, previous year papers and mock papers. There are many good institutes available which provide mocks for the same like Made Easy, Ace Academy, Gate Academy, Gate Forum& etc you can choose the one which clears all your doubts and which are easy to understand.

Hope this helps!!!
Good Luck!!!