Regarding scoring of good marks in Board Exams, it is not so difficult.

You have to stick to few important tips:

1. Firstly, study regularly, take out time for at least three subjects in
a day. Work more on those subjects, in which you feel you are weaker than other subjects.

2. Do not leave any subject for more than 2-3 days. Every subject should be taken up for study at least in every alternate day. The important and difficult ones may be taken up everyday.

3. Devote at least 6-7 hours for self study.
But do not cut down too much on your sleep and enjoyment. Take out a bit of time for relaxing and entertaining also.

4. Whenever you study, don't sit for too long continuously, you can also take one or two short breaks of 5-10 minutes during a continuous stretch of 3-4 hrs. of study.
This will help in maintaining your interest.

5. Be in touch with the CBSE previous years papers, sample papers etc. Keep on looking what has been the pattern of CBSE and what type of questions are generally asked. Also refer to their model answers.

6. Whenever you give a test in school and obtain marks, just go through your answer sheet seriously and see where marks have been deducted and how can the errors be avoided next time.

7. Take proper care of your health and hygiene. Do regular exercise, take more of green vegetables, milk and other nutritious food. Do not get tensed.

8. Although you must stick to NCERT books, but in science, maths, you must do some extra questions also. You can purchase a good book or question bank for that.

9. Be in contact with your teachers and ask them to evaluate yourself.

10. At the end of the year, do at least 8-10 model test papers for each
subject. This will help a lot.

Just keep working towards your Goal and keep on evaluating yourself.