I was not good at math before, so the only way is to do more and practice more. Since your classmates are better than you in the Olympics, you can only reap the fruits like others by being a stupid bird that flies first and paying more than others. I recommend a material called Exploring and Applying New Ideas, written by Huang Dongpo. The above topics are difficult, but almost all of them have detailed solutions. You should try to choose some difficult topics and study them slowly, so that you can become yourself. I have finished all these materials, and the math exam is the most controversial.