i m in high school this year , iwant to know how and when I have to start my neet preparation please tell me Guru ji

NEET syllabus will be revised and reduced in 2021. Which means if you are in High School, by the time you appear for NEET, the syllabus will be reduced and revised. And we do not have clarity about the topics that might be retained or the topics that might be removed from NEET Syllabus. In such case, sticking to NCERT makes sense because you do not go overboard and focus your time and energy on the topics that might not be necessary as well. So stick to NCERT atleast until MHRD ad NTA officially declare revised NEET syllabus.