Hello Ankit,
If you want to get upto 95% in 12th class, and not having studied in 11th. It is going to be tough. You need to attend every class and pay maximum attention while taking notes in class and re-reading once you get home.
Clear all your distractions phone,television or computers/laptops. Go out for a walk regularly to practice mindfullness. Try Meditation.
If you want to join a coaching center for an entrance exam, don't. It is very hard to manage both.
Hope that helps and feel free to ask if you have any more queries. Best of luck!
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