Everyone has their own choice of books. The two books that are used the most were

1.) Chemical Engineering for GATE -Ram Prassad

2.) Arihant's Chapter-wise Previous Solved Paper: Chemical Engg

One more book I followed for objective type questions was the book by O P Gupta (Although not as much as the previous two).

For text books I used

1.) Mass- BK Dutta

2.) Heat-BK Dutta

3.) Fluid- NPTEL video lectures by Dr V. Shankar

4.) Thermo- Smith Vennes

5.) Process Control- Stephanopoulos

6.) Chemical Rxn Engg- Levenspiel

For Minor topics Like Mechanical Operation, Economics, Process design etc I used theory segment of Ram Prassad.

I will suggest follow the text book that you are most comfortable in, it hardly matters.

As far as tips are concerned - I can tell you three mantras that worked perfectly for me

1.) Make a Formulae Book- I started preparing by the mid of November while I was working with an MNC. So first 30-35 days I studied the major topics ( The six topics listed above) 3-4 hours daily and made a formula book out of it. Mostly I solved examples from the text books I have listed. I would suggest the same for you too-Don't spend much time reading as it wastes a lot of time and energy, instead try solving text book examples and exercises, that will clear your doubts.

2.) Practice Problems- Do as many problems as you can do. During the first 30-35 days of my preparation- I would complete studying a topic within 3-4 days and then devote 1-2 days for practicing problems. By mid of December, I was mostly solving problems from ( Ram Prassad, Previous Years Papers, OP Gupta). If I got stuck in some problem, I would refer to my formulae book. If I couldn't get it in my formulae book, I would go to text books and/or NPTEL.

3.) Keep Refreshing and updating your concepts- Read your formulae book over and over again. Besides, whenever you find some important concept or trick while solving problems, note it down in your formulae book.

One more point, which may not be that important yet I would suggest, is to join some online test series. The online test series that are available for chemical engineering are not very useful yet they give you an insight of the exam web interface and also of the online calculator