Dear Chandan, 12-14 hours is more than enough because the Brain can endure only so much. We shall not burden you with more Do's and Dont's. We shall give you some tips to keep the momentum going. Dont stress yourself because you do not want to drain your brain too early. Make sure you keep changing the pattern of studying too often to keep your brain active. Every week make sure that you attempt atleast one mock paper. Have post-it's and flash cards bearing important formulae in all subjects and keep memorising them as often as you can. Allott 2 hours per chapter and per subject and change the subject every 2 hours. That will keep you on your toes and keep you active and engaged throughout the whole day of preparation. Do not forget to keep yourself relaxed and hydrated.