Books come first. Choose a good book, like Guo's, which is easier to understand. Read through a book first, and then find out what you really don't understand by querying or browsing other books. The topic still needs to be practiced. If there are many problem sets, choose one that suits your level. This is very important for understanding and consolidation, but personally, it is relatively simple to choose theoretical mechanics. Electrodynamics is the second, and quantum mechanics is the most difficult. But every subject has advantages and disadvantages. For example, theoretical mechanics is easy to understand and difficult to do, but so is your competitor, so it is not easy to distance yourself. Electrodynamics is a little bit in the middle, but when you choose a major, it is very limited, because the specialized course is electrodynamics, which is generally less. If you choose quantum mechanics, it is very abstract and takes a lot of effort to understand. However, there is also an advantage that its theme is monotonous, that is, it has changed several typical examples. No matter which unit, there is not much difference. There are few topics in the postgraduate entrance examination papers. Take the Chinese Academy of Sciences as an example. Generally, there are five big questions, each with 30 points. In other words, people who choose quantum mechanics face two extreme situations. Learning well can be as high as 140. Once it is not, many of my classmates are faced with this situation. So I suggest you think about which unit you want to enter first, and then consider the problem of professional courses. You'd better take a look at the real questions of the school or college you want to take the exam a few years ago. This will be of great benefit. Each subject has its own advantages and disadvantages. I hope you will consider it carefully. The mathematical requirements of theoretical mechanics are relatively minimum. Mainly the high number part. Electrodynamics and quantum mechanics require linear generation besides high numbers, especially quantum mechanics. The most important thing in electrodynamics is relativity, and the most important requirements in mathematical calculation are point multiplication, cross multiplication and gradient of vectors. There are two ways to explain the core of quantum mechanics, one is Schrodinger equation and the other is Heisenberg matrix mechanics. You can imagine.