Sir Im studying in St. Stephen's college doing BSC(physics)hons. in 1st year.How can I prepare for iit advance with my regular studies.

you need to measure your performance by your study planfor the day. You need to establish definite goals to be achieved in a day, in a week, and in a month.
Your daily goals will need to include:
topics you will study,
preparing notes for the topics you have studied,
solve practice questions or numericals related to the topics, and
solve at least two practice papers, sample papers, mock tests, or IIT JEE past year papers a day.
It used to take me 5-7 hours to complete my daily goals. Use your clock only to see how much time you took to solve the tests.
good luck!