Hello aspirant ,

As per your mentioned query , you have to mention the stream for which you want to ask the reference e-books so that i will suggest you the books for your preparation. Now , come to the ques of how to crack the GATE exam so , i would like to highlights some preparation tips that will helps you in your preparation.

1. First of all , analyse your whole gate syllabus as what concepts and what subjects are coming including your aptitude part.
2. Now , make time table according to your comfort in which give more time to those subjects or topics that are tough for you . So , you can practising those topic more .
3. Study consistently as consistency is the key to success . Try to solve the previous year question papers so that you have an idea lf questions that are coming.
4. Try to solve one paper daily so that you can manage your time according to your exam.
5. Revision is the most important part so revise your concepts weekly.

For the reference books , as you are not mentioned the stream , so i will suggest you to go through the given link :

https://engineering.careers360.com/articles/what-are-best-books-for-gate-preparation

I hope this will be helpful for you.

Good wishes !!