hi,

nice to see that you want to start the preparation from now itself . the first thing you need to do is go through all the concepts of NCERT textbooks and then in addition to them go through the other reference books and solve problems . the thing you need to remember is never feel shy to get your doubts clarified . and also a tip to note down all the basic concepts i one notes which will be helpful for your revision .All the best for your future . 

Dear Harsh, if you wanna crack the jee-main exam as well the jee-advance exam then you need to focus some points - 

1. first of all cover up 11th NCERT books(PCM) because of the syllabus of jee-mains and the advance within NCERT books(11th + 12th).

2.go through the previous years papers and solve them side by side of your study.

3.you can learn through online materials platform like youtube.some channels are good and provide better education free of cost.

some channels are - 

etoos education, Mlearning India, khan academy etc.

4. you can join offline coaching institutes like Allen, resonance,fittjee etc.

all the best for your future.