Hello! If you looking for preparations of GATE it is too early beacuse right now you have to focus on basics which you will be studying in your 3,4,5 and 6 semesters probably. 

You can refer this link: https://admission.aglasem.com/important-books-for-gate/

There are so many books for preparations but I suggest you to First try to build your concept and try to understand the application part of your branches like cse, mech, ece etc.

Please mention your btech branch