The most important thing in writing a composition is to grasp the center and then imagine boldly around it, just as you said.
When you write this article, make sure what you want to express. Obviously, if you just want to expand your writing style, you won't jump out on the test paper. You are writing a composition on the test paper, not a serial novel. If you want to get points, you have to grasp the reality and be close to life. If you unfold the story, it will appear empty. When you lament the joys and sorrows of the ancients, you can also compare yourself with them and sigh that you still take us as time. A generation compares the ancients and laments the gap between now and now, and so on. In short, write a composition, grasp the center, expand your imagination, use phrases (words you are familiar with), have clear paragraphs and keep the content close to life.
Okay, that's too much. The landlord can see for himself.
I hope I can help you.