Hello subrahmn,
This is very tough choice which one you ask.
First off all,  your basic is very clear of your core branch.
You have to know syllabus and prepare your self according to your knowledge and preparation of the subject.
You can try online study material and buy made easy note and booklets.
After preparing self, you must  join test series.
After that you should know about yourself.
Good luck.

You should know syllabus well, exam pattern amd use top recommended books for grasping all fundamental and advanced concepts  

Practice more than 0mpcks and go for group dohbt solving. 

Make sure you have strict timetable and you do follow it. 

https://engineering.careers360.com/articles/how-prepare-for-gate-without-coaching

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