If you are in second year no need to prepare explicitly for GATE concentrate on your subjects and try to solve the objective questions that appeared in GATE of your current semester subjects of GATE syllabus and try to make short notes for each subject.(This will give you an idea of how deep you have to prepare for each subject for GATE).
Later after third year(by now all the subjects of GATE syllabus will be completed) you can purchase any test series of coaching institutes and keep solving them.
If you follow this I'm sure you can crack not only GATE but also any PSU examinations like BARC, ISRO,BEL etc. without any need to attend any coaching institite.