I'm no expert, but I did prepare for Mains and Advanced for the exam in 2015. I hope you find these tips useful.
1. If you go to coaching classes, try to keep up. Out of all the three subjects, physics is easily the most difficult as conceptual understanding in physics is vital. If you fall behind in your coaching classes, things will become hard for you down the road.
2. Make full use of HC Verma. The man is still famous after over 30 years since the first edition of 'Concepts of Physics' was published because no expert author has come up with a better alternative. In fact, many JEE toppers claim every year they solved HC Verma atleast twice.
3. Do not surround yourself with too many books. Consult a set of maximum of two reference books besides NCERT.