For cracking competitive exams you have to develop the spirit to study and enjoy whatever you study. Firstly I should tell you to analyse your thoughts and aim. If you want to crack iit then you to pay most attention to physics chemistry and maths. For medical you have to go for physics chemistry and biology. In competitive exams upto class 10 full science(pcb) and maths are required. First you start loving your studies and dont take it as burden. Secondly you buy few books like mtg foundation course physics,chemistry,maths and biology of class 9th. Also refer class 9th r.d.sharma and ncert for maths. These books are the best for competitive exams. Also take a good coaching like fiitjee if you can. Its not very important to take coaching upto class 10 but it will help you. Please approve my answer by clicking approved if you liked it. Good luck!!!!!