I would suggest you to go through the below tips - Follow NCERT strictly and some standard refrence books.
Make notes Separately for each subject and remember it, revise it, try to wake up early in the morning and study.Make a routine follow it strictly and make sure that you have all your important subjects in that routine.Follow your teacher's carefully and attentively because in class they tell the format or manner in which you have to answer in your main/12th examination and also make sure that you follow them.In board exams the examiner checks whether you have undrestood all the concepts or not that's why they do step marking.Step marking is very important because in CBSE it helps in obtaining marks.So Plan your day from today itself.Good Luck!!!