Hello 

Mansi 

Good i will give you a good plan 

Now your in 11th class if you start studying now it is well and good please study properly ncert books and later on for physics you refer H C verma , chemistry O p tandon,  mathematics airhant is good reference books please watch the nptel videos for more understanding of difficulty topics please study atleast 10-12 hours per day so that you xan crack the top IIT's for sure and also please make a perfect plan or time table for best preparation don't waste your time please utilize every resource for your IIT preparation only 

I hope you understood 

All the best