Dear Mohit,

In order to score 80% marks in your board exam you need to make your proper time table according to your strength and weakness. Devote time in each subject as per your strength and weakness. If you want you can set your daily and weekly targets. 

Give proper attention to the topics which are important for your boards exam. 

Your text books are very important as syllabus is based on them. Solve all the exerciss which are given at the end of each chapter.

Refer previous year papers for your practice.

All the Best!!