GATE

There are very good books available for preparing GATE examination. But in order to have very good exposure and good understanding of all the concepts, you need to refer more than one kind of series. So based on that experience, below are my recommendations to crack the GATE examination. For CSE students:
1. GATE tutor 2018 Arihant publication
2. Trishnas: Computer Science and Information Technology
3. GATE 2018: Computer Science and Information Technology
For ECE students:
1. A Handbook on Electronics Engineering (highly recommended)
2. Arihants: GATE tutor 2018 Electronics and Communication Engineering
3. Made Easy GATE 2018 Electronics Engineering
For EEE students:
1. Made Easy: GATE 2018 Electrical Engineering
2. Made Easy: A Handbook on Electrical Engineering (very useful)
3. Trishnas: GATE 2018 Electrical Engineering
For mechanical engineering:
1. Made Easy: GATE 2018 Mechanical Engineering
2. Made Easy: A Handbook on Mechanical Engineering (useful one)
3. Arihants: GATE tutor 2018 Mechanical Engineering

In my opinion, this totally depends on you, as how much time you want to spend and also how much potential you have i.e. I am telling you my strategy. My friend and I decided to take GATE, and we are in the final year of graduation. So, our strategy was, we purchased the book of GATE 2019 and also previous year's paper, as it's syllabus contains all previous years B.Tech subjects. So, we will go through one subject and after that, you can solve previous year's questions according to it. There are also some websites which provide free mock tests where you check your knowledge or preparation. At last, I would like to say that it totally depends on you as how much you are dedicated to it and how much efforts you are applying to it. So, work hard and do lots and lots of practice. Hope this help. Good luck.