It is as easy to understand as it is difficult. Well, this is not a puzzle; we are talking about Physics; one of the subjects in IIT- JEE exams. It is famed for making students love and hate it alike because if you get it right understanding will not be a problem and learning will become a cake walk. On the other hand if your brain fails to register the concepts well, it can give you sleepless nights.
For clearing IIT-JEE what is needed is a clear understanding of the subjects involved because this exam tests the students on their understanding and application of the fundamentals. The questions are such that you have to apply your concepts and get answers in a limited time. While preparing for Physics:
1. Read the topics thoroughly. It is very important because to get a clear understanding you must build your base in every topic. The whole syllabus builds up on the various topics studied and if you fumble getting even one misunderstood it will affect your whole understanding.
2. Get the concepts right. Building the right concepts is the biggest problem faced by students while preparing Physics. Therefore, read proper books and consult your teachers if you are facing problems in understanding the topics involved.
3. Ask as many questions as you feel like because this is the way to getting your doubts cleared and building your base. Though you may be ridiculed for being the Mr. Question Mark it is better to called be so than to have questions raised at your capability afterwards.
4. The story does not end with understanding of the topics. It is as important to learn their application as it is to get their understanding. Therefore, practice as many numericals of different types from different books as you can.
5. Stick to a few books only for building your concepts. Since, understanding is the keyword, referring to the proper books is very important (and it does not require reading loads). However, for practice purpose you can refer to as many books as you want. In this case it helps as much as you can lay your hands upon.
Thorough reading and proper concept building will sail you in the right direction as far as Physics is concerned. Getting the concepts right will make your chances bright. Good Luck.