How to answer this topic better
The answer is stronger when you show progress and effort, not just the final result.
Explain the goal, the difficulty, the turning point, and the final impact.
You can record an answer, review the transcript, compare it with a stronger sample answer, and retry the same prompt without losing the main idea.
A goal I achieved was improving my English enough to feel comfortable speaking in class. At the beginning, I understood many things, but I was afraid to speak because I thought I would make mistakes. I set a small goal for myself, which was to speak at least once in every lesson. It was difficult in the beginning, but I kept trying. After a few months, I noticed that I felt less nervous and could express my ideas more easily. This goal mattered to me because it gave me confidence and showed me that small daily effort can create real progress.
This answer is around Band 6 because it has a clear sense of progress and purpose, but the language could still be more flexible and expressive.