Hi Sunita. I will tell you how u can prepare for ur board as well as entrance exams 

Physics and chemistry - it's all about understanding the concepts , use a good book in addition to ncert , under the concepts ,solve as many questions as u can , at least 300 to 500 per chapter , check , analyse and rectify your mistakes. That's the mantra..work smart

Biology - ncert is Bible here..just read thoroughly page by page and cover to cover , around 300 marks /360 in NEET is just from that..if you have any difficulty any where , make notes , repeat again..understand and clarify.be thorough with your concepts.