Hello

for completing your 12th with good marks you have proper planning

• Follow a proper schedule: sleep and wake up early have a breakfast and Study well
• Make a time table of full-day for study
• Exercise daily so you will feel relax whole day
• Do meditation and yoga daily
• Solve sample paper : there is a mantra without practice you won't achieve anything so practice daily
• Revised everything which you learn last night
• Avoid distraction
• Be focused in your studies
• Work on your weak areas
• Stay healthy: eat healthy food
• Do group discussion with your friends

I hope this all tips helps you

Good luck