Do planning - The college allows you to keep around 75% attendance. So you can miss about 25% of the lectures. Plan those 25% well.
Try to Make practical schedule - Do not make a week schedule. Make only three days schedule and try to follow it religiously.
Study during college time - You spend a lot of time everyday in your college. If you do not utilize that time for GATE/CSE, it will become difficult. Study GATE even during college time
Study theoretical subjects - Since solving GATE numericals may not be possible in regular college classes, you can study theoretical subjects which do not require much mental focus.
Selection rate of only 15% - Around 6-7 Lakhs students appear for GATE every year. Only 15% of those students crack GATE i.e. score above 25 Marks.
Pay attention to class as well as study - After every few hours, pay a little attention to what is going on in class so that at least you have an idea of what is being taught.
Conceptual and Numerical Part - If you are preparing well for GATE, then many subjects taught in your college will be easy for you as GATE preparation will consist of conceptual and numerical part.
Cover Class Material Every Week - For subjects which are not in GATE, try to cover class material every week only during college hours.
Re-revising on whatever you have studied - Focus on revision and re-revising on whatever you have studied. Take All India Mocks and FLT every week and Analyze them thoroughly.