This is the question which every twelthie ask.

Okay first thing don't study like donkeys I mean don't study like 12-11 hours.

Make a time table, study 7-8 hours.

Practice and revise as much as you can

Prepare a time table divide your time in 3 study slots like first study slot is from 9-11 am

Second 4-6 pm

And third 9-11pm

Sleep well, take balance diet.

And don't panic

Good luck