This is strictly for the final year students or the ones who passed out because if you start preparation for GATE earlier than that you will just drop it. I want to make it clear I myself did not score any good marks in the GATE-2015, There were 3 reasons for it.

I was already placed and wanted to enjoy my final year.

I did not want to go join any PSU (I did fair amount of research before coming to this conclusion)

I did not want to do my higher studies in India.

SO why am I writing this post, because even though I did not even touch the book I was able to clear the GATE and get a rank, and I believe my experience will come to students who are sincerely and seriously preparing for GATE-2016.

In an engineering college there are two types of students who can score well in GATE:

The ones who are highly conceptual and understand Chemical Engineering to its very core (I know two such students-my batch mates one scored AIR-18 and the other-138). This type of students generally don't prepare much, the amount of time they spend studying is less but the effort and concentration they have and put into use at the time is tremendous.

The second type are who have to read a lot to get the grasp of the subject, in this case a lot of time is required and you will basically miss out your final year masti upto the point you give the exam.

I will just give an overview of what and how you should start preparing. Any person who will start preparing for GATE should start with the NPTEL lectures available on the internet and then move on to the books.I have listed out the important subjects and from where to prepare for them.

Mass Transfer, it is by far the most important subject for a chemical engineer-this subject will be useful for your placements too. Prepare notes and study from Mass transfer operations by N Anantharaman(This is a book written by a senior Professor of NIT Trichy and he is the best we have, the book is highly compressed and will help you get an advance start, although treybal is a good book it takes a lot of time to cover all the topics), and start practising questions from Aptitude Questions and Answers(A free site and it helps a lot with your placements too). After you complete the preparation do not leave it aside-revise every day for half-one hour from the notes you have prepared.

Fluid Mechanics Follow McCabe and smith it is most probably the best book for Fluids, As what it is for Mass Transfer you need to keep on revising the topic and be thorough with the basics up to an advance level. Make notes for this subject as well.

Heat Transfer, This is an easy and high scoring subject, follow Binay K Dutta, it is short apt and most probably the best book for preparing for competitive exams.

Chemical Reaction Engineering , do not read from fogler, no such high level questions are asked in the GATE nor any other competitive exams. follow Octave Levenspiel and solve questions from Indiabix or any other GATE preparatory book (I prefer Arihant over others).

Thermodynamics Follow KV Narayan and be thorough with the basics, conceptual questions are asked from these topics

Process Dynamics and Control Only basic level and Level 2 questions are asked which could be solved if you have the basic understanding of the topic follow coughanowr

Mechanical Operations, Unit Operations, Equipments, and Basic Chemical Engineering follow McCabe & Smith

Inorganic and Organic Chemical Technology, Petroleum, just do questions from Arihant and Indiabix-the questions are repetitive and actually studying these topics will be a waste of your time.

Project Economics I did not even read the topic before writing GATE it was in the last semester that we had the topic, it is easy so you can read it from NPTEL that would be enough or just follow your professor's notes.

Process Calculations Follow Himmelblau or you can actually follow a book written by my professor N Anantharaman (It is very compact and will require far less time) the questions asked from this topic are actually very simple and easy if you remember all the terms and equations.

This is very good to know that you are so serious about your Gate preparation but as per my view it is better to start your preparation in your 3rd year because first 2 years of B.Tech is the ideal time to make all your basics concept clear and strong. Apart from this, below I am providing Gate preparation tips which you should keep in your mind whenever you start your preparation  -

1. Know the syllabus very well.

2. Read standard books only as there are many books available in the market so it is advisable to use the books which make all your concepts clear and which are easy to understand.

3. Understand the weightage of topics properly.

4. Proper Revision plan should be followed.

5. Mock Tests and Practice Tests should be done as this will help you to learn time management skills and this will also make you familiar with the exam pattern.

For reference, you can go through the below link -

https://engineering.careers360.com/articles/gate-how-prepare-for-computer-science-engineering

Good Luck!!!