The main thing is that you have to build your concentration level, then only you can stay focused on your goal. I would like to say that please limit the study time between 10 to 12 hours and please increase your concentration and speed of reading, understanding and solving the problems then you will not face any kind of difficulty.
For the preparation of exam, the most important thing is your confidence after that you should know the whole syllabus and make your plan properly for learning new chapters, solving the numerical and revision. All three things should be part of your preparation strategy in daily routine.
Your basics in Physics, Chemistry & Mathematics should be very clear up to 12th std. You should read the NCERT books for basics. Then HC Verma for Physics, RD Sharma for Mathematics, OP Tendon for Physical & Inorganic Chemistry, and Organic Chemistry of "Arihant Publication" for detail or extra knowledge. In this way, you can prepare well for the
MHT CET 2019 examination.