You can follow below points to prepare for JEE/KCET along with boards exam-

Focus on concepts & theory

While JEE Main and KCET is about practice, board exams are about theory. Make sure your concepts are clear you can take help of NCERT books for that.

Revision

In board exams, revision is the key to scoring marks. Its also important for JEE Main that you remember all the formulae so that you dont miss on the easy questions.
You can focus on the chapters which carries more weightage in the exam of JEE Main/KCET and make sure your revise them thoroughly.

Time-Table

Make a proper plan. So, that you prepare for board exams to optimize your JEE Main and KCET preparation.

Complete the syllabus

Try to complete your whole syllabus dont miss any topic. JEE Main has questions from all the topics. This approach will help you ace your boards as well as your JEE Main exam because you will have studied everything clearly.

Exam pattern

You should be aware of the exam pattern of JEE Main/KCET and boards exam and level of questions asked in both for that you can go through previous year papers.

Mock Test Series
Try to solve complete mock test series to know your strength and weakness and where you stand and how you can work upon them.