Hi Deepak !
If you're targeting
IIT JEE 2012
and other Engineering Entrances
then you need to study hard.
You already are in class 12th, so from now on, every topic that you cover (in any of the three subjects), try to clarify every concept related to it. Also, if you can manage to cover your class 12 syllabus on week days (per week basis), then on weekends you can try to brush up the concepts of class 11th.
So, target all the engineering exams like- WBJEE, Odisha and Karnataka engineering. And try to strengthen your grip on the topics that you study from now on.
All the best !