Here is good advice from vikas garg (AIR-3, 2007 CS) he was IISc student and now phd student of UIUC

Here is a description of what I feel is important for getting an opportunity to study at the premier research institute of the country; students at large may benefit from it:

1) Clear your basics and fundamental concepts. There is no point mugging up each and everything; need to develop the ability to think rationally.
2) Do as much practice as possible. Specifically try to solve as many test papers as you can within the stipulated time, this will instill a sense of confidence in addition to improving speed.
3) Don’t try to run through the paper. 3 hours is a long enough period and time won’t be a constraint should you know the things.
4) Avoid making silly mistakes. It’s imperative that you get right most of the problems from topics that you are comfortable with.
5) Keep solving GATE papers of last 10-15 years. Monitor your progress as you master more topics from different subjects.
6) Believe in yourself and your abilities. If anyone else can do it, you can most certainly as well.

Another important point: Go through some standard textbooks without haphazardly chasing all the study material in this world!! I found the following books useful:

1) Computer architecture: Henessey & patterson, Morris Mano, and William Stallings.
2) Discrete mathematics: Kenneth Rozen, Kolman-Busby-Ross.
3) Finite state automata/theory of computation: Michael Sipser, Peter Linz, and Hopcroft-Motwani-Ulmann.
4) Compilers: Aho-Hopcroft-Ulmann (The Dragon book).
5) Data Structures/Algorithms: Mark Allen Weiss (excellent), Tanenbaum, Cormen et. al (an absolute must), Kruse-Tondo-Leung, Sedgewick, Brassard. Horowitz-Sahani etc. for specific topics only.
6) Operating Systems: Galvin-Silberschatz (standard book).
7) Computer networks: Behrouz forouzan, Kurose.
8) Mathematics: No specific book—> book for discrete mathematics covers most portion of maths also.
9) DBMS: Korth-Sudarshan, Elmasri- Navathe.

Interview for EE students http://soumenmandal.blogspot.in/search/label/INTERVIEW , also check Gatecouncellor site for many interviews.

people can read these as a general guideline

http://www.gatecounsellor.com/interview-questions/