See dear your in the age where iit topper starts  doing their preparation   so  you should do  studies 3 hours 1 hours per subject  daily then it will be easy for you  to understand 
						

							
 
Dear Aman,
You can start by completing your course thoroughly, making proper notes. The concepts you are gonna study in 11 and 12 derive their bases from 9 and 10 only. 
However right now you should not be very focused on iit jee preparation. Its good to start early but iys equally important to be healthy and happy. Enjoy your other subjects as well. If you don't attend any tution classes you should be able to spend 4-5 hrs of the evening to your studies. You can start from 2 hrs gradually increasing the time. Try to devote 1-2 hrs in the morning after you wake up and before going to school. Morning time is best for learning new topics 
Daily revise what you learnt in school. Weekly revise the topics you learnt that week. 
 
Hopefully this helps you. All the very best for your future