You want to get better results in the English language tests or exams. Therefore, you want to improve your writing.
To improve your writing, you should practise more.
As you write more often, you raise your confidence.
As you write more often, you think more. When you think more, you generate more ideas to write.
As you write more often, you expose yourself to the language. You can detect your errors more easily by reviewing what you have written.
Try to have a look at some pictures and start writing. A short paragraph or a few sentences (correct or not) will help you improve.