Gate Syllabus includes the same courses that you have in your Academics.They are:
The First Year courses include C programming,Differential Equations & Transforms,Matrix Algebra & Numerical Analysis,Probability,Calculus and Basic Mathematics.
The Second and third year courses include Data Structures,Operating Systems,Digital Logic Design,Computer Organisation,Computer Networks,TOC,Compiler Design,DBMS,Design and Analysis of Algorithms.
You better concentrate more on these courses which are also a part of your academics.Go through the online tutorials and also the video lectures.And if necessary,do take GATE coaching from any good institutes so that you can practice to the maximum extent and also you can study the subject in depth.According to the proverb "Practice makes man perfect",do practice more inorder to achieve success in your examination.