Personally, I found physics to be the most interesting subject when studying for IITJEE. Physics is about understanding the world around you and does not depend on remembering a lot of things.
In perspective of IITJEE, the first few chapters in physics i.e. Kinematics, Laws of Motion, Work and Energy are particularly important as applications of them can be found in almost every other chapter. If you have trouble in these chapters, you will find later chapters more difficult. Never rote learn a formula or problem in physics, without understanding it. Try to practice different kind of problems, so you know beforehand the methods used for particular type of problems and that will help save time in IIT-JEE.
If you love physics, you can try solving books like I.E.Irodov as the questions in such books expand your understanding of physics. Note that most of the questions in such books are outside the syllabus and level of IITJEE exam, and thus you don’t need to do them. But if you have solved a book for IITJEE physics, try to solve Irodov. It might be fun and will definitely enrich your knowledge of physics.
One of the important thing to take care about is whether your answer makes sense or not. Based on everyday experience, you could have a have a pretty good idea of the range in which the answer can lie in most questions. So if you get outrageous answers, (like a very large distance for a question in kinematics with normal inputs) take a look at your solution again, there might be a mistake. Also, take care of the units in the answer. After all, a physical quantity can’t be just represented by number without any units. Make a habit of putting the units with the values at every step of the solution, as it avoids errors when changing between units. Also, use dimensional analysis as much as you can to verify your answer. If length is asked, your answer must have dimensions of length.