Let me talk about my own experience. The second-level exam was good, and the foundation of vocabulary and grammar was solid, so I went directly to teach myself the textbook of 1 after the exam. At first, I bought new Japanese 3 and 4, but after reading it for a while, I found it very troublesome, so I went directly to buy books on grammar and vocabulary. I bought a set of 1 level guidance books published by East China Normal University, which can be said to cover all the required grammar and vocabulary, and even put forward the contents of possible propositions outside the examination syllabus, which I think is very good.

As you said, the first-level grammar is very complicated. A point can have several meanings, and a meaning can also be expressed by multiple points, which is a bit difficult to accept at first. But my method is this: the grammar and sentence patterns in the book are compiled according to the meaning classification. So I also took a photo of the secretary smoothly. First of all, after learning for the first time, read every sentence carefully, including their meaning, connection method, fixed collocation, special precautions, example sentences, etc.

For example, the sentence pattern "んがため" (に) is very special, so we should remember that it should be placed before verbs, and so on.

After the first pass, we have to do further work, that is, sorting out. For example, the distinction between sentence patterns with similar meanings. These should be done through a large number of example sentences, which can not only cultivate a good sense of language, but also deepen the understanding of sentence patterns. For example: たとたんに, たかなぃかのぅちになり, after the second pass. Next, I will do more exercises. If I have time, I can also read Japanese books. By doing the problem, we can find the problem and grasp some details, so that we can 100% master it.

To tell you the truth, when I do the first-level grammar questions, I am basically right. I think this is due to the above systematic method.

For reference.