You should concentrate on boards exam and MHT CET exam both. You should prepare for both the exam simultaneously.

MHT CET and your board syllabus is same. Only difference will be MHT CET questions will be of advanced level as it's level is raised to JEE Main.

In MHT CET 11th class will hold 20% weighatge and 12th class will hold 80% weighatge and there will be no negative marking.

To score good marks in your boards and MHT CET it is very important that your basics are clear. It is very important that you cover your textbook.

You can make your time table. Make a list of the topics which you have to complete. Try to cover important topics first which carries more weightage in the exam. You can also prepare your important notes which will help you at the time of revision. Set your daily, weekly amd monthly target.

Practice is the key to sucess. Solve as much as MCQs for your practice. Refer previous year papers for your boards and MHT CET exam for your practice.

You should also solve complete mock test series to analyze your preparation level and to know your strength and weakness. So, that you can prepare accordingly. Work on your time management as well as it plays a important role.

Revision is very important to score good marks in your exam. You should revise daily.

All the best for your preparation and exam!!