Thanks for asking Sathvika.
I have cleared IIT JEE with AIR 904 in 2005 and did computer science graduation from IIT Guwahati. I did the following during my high school,
Understanding concepts deeply
IIT is not about how much you know, but how deeply you understand a particular topic. I felt the same thing even during my graduation in IIT. Don't give up those concepts which you don't understand. Try to get answers from your brothers/sisters.
Reading textbook on my own
I use to read textbook on my own before the teacher teaches that particular chapter. That helped me stay ahead. During the class, I used to concentrate more on those aspects which I couldn't understand on my own.
During my 8th, 9th and 10th, I used to do a lot of hard work and study very late in the night. Although I feel that much of hard work is not required, staying for long hours helped me a lot in my 11th and 12th standard. I hardly slept in any study hour during my intermediate which helped me to crack IIT JEE