This is my story on how I prepared for CBSE AISSCE 2012 in the last two months. I was a computer science student and I was done with my 2nd pre-board exam on the first week of February 2012. It was the last preparatory exam offered by my school prior to the CBSE board exam which started on March 1, 2012. All my 12th scores were around 60 - 70% which hit rock bottom of 54.6% overall (PCM + Eng + CS) in the 2nd pre-board exam. So I had almost one month between the first week of February to the first exam English which was on 1st March, to do something to turn the results around. If you are from India, you will know that this will be accompanied by a great deal of pressure from parents as well.
CBSE board exams spans over a whole month. So I effectively had around 2 months to prepare for the last exam which was Computer Science in my case on 26th March. Keep that in mind. So you have to concentrate 'more' on the Initial exams in February. So this is one thing I did. At an average, I got around 5-6 days between each exam. Last two days before a specific exam was solely dedicated to that subject.
Most of the questions they ask are either directly from it or variations of those questions. If they ask out-of-syllabus, we can't do much about it in a month's knowledge. First, read the NCERT chapter by chapter as much as possible. This is the most difficult part. When you get bored switch subjects to make you going again. Remember, I didn't have much time to spare either. I won't say a fixed number but try to spend as much time as possible with enough breaks.
While you go through the chapters, make handwritten notes of the concepts you feel is important so that you can go through it again easily any time of the day. I used to fold an A4 paper vertically and write important stuff on both sides which I continue to do even now, before my exams.
Initially this is going to kill a lot of your time, but once you get it going you will be able to solve questions easier. Try to solve the questions by yourself. I don't find any harm in referring to guides for solution after you have given some initial thought as well.
I wouldn't suggest the internet, yes it might be easy but using computer used to distract me and kill my time a lot. I used to call up my friends. You can call up your friends or faculties as well if they say it is okay. Make sure you clear 4-5 doubts together so that you don't disturb your friend always with phone calls. Write them down as well.
It is very important that you attempt some of them at-least. The more you do, the better. You will get used to the CBSE exam pattern and the difficulty of questions for each subject. And there is good chance for the questions to repeat.
Make sure you do a good revision of the subject and see to that you revise the most important set of problems. Make sure you get around 6 hours of sleep on the night before each of the exams. I used to sleep early by 9-10 pm and wake up early by 4 am to do one final revision. You can do wise-versa as well.
Finally keep your cool just before you enter the exam hall. Leave no stone un-turned, attempt all Questions even if you have no idea about the answer. After you finish your exam try your best not to discuss the answers with your fellow schoolmates. If you get to know something went bad it might affect your motivation to go on. This is one thing I could not avoid completely.
In the end, I have tried to follow most of the points above, and I was able to score 92% in the 2012 CBSE boards which were decent enough for the CBSE standards. No one has ever asked me my 2nd pre-board score nor mid-term scores. These 5 exams are going to out-weigh how you performed in your last 2 years, but this exam alone doesn't define your academic capability at the same time. All the best.