Hi harshal joshi, 

Great to hear from you that you are beforehand concerned to prepaee for 12 board exams. The only key to get good marks is understanding each and every concept clearly instead of cramming it. Regular practice adds up alot. Learning everything at last hours or days is not of sufficient help as we cant understand everything in just few days. Taking help of previous year question apaers will help you a lot. The only thhing to decide your marks is your hardwork and practice. So start doing you preparatio fron now onwards and best of luck.