Hii Likith...Having such a goal is really good. For getting a M.Tech seat in top colleges with good gate score. Firstly go through the portion. If your are presently doing btech you can focus more on core subjects(gate subjects). But just doing what your prof says in class ins not enough. You need to go through the text books and mainly through the previous years question papers. This all will give you a clear picture. you need to solve more number of mcqs and need to strong in the concepts. Hope this helps you.