In order to score good marks in physics to clear your IIT make sure you build your basics strong. Try to work on your concepts and build your fundamentals strong. 

You can take help of NCERT books. 

After, completing your NCERT books you can refer other recommended books

Focus on the topics which carries more weightage in the exam. You can also solve as many as MCQs as well for important topics.

Refer previous year papers to understand to type of questions asked in the exam.

Al the Best!!