forces you to reflect on specific writing experiences that have contributed to your current skill, and it forces you to set a goal of some kind.

Be truthful. Your instructor isn't so much concerned about what you are writing about. They want to see how you write about it. Be specific with your examples, and be specific with your language. Don't just say "one time" or "a few years ago." Be specific. For example, say "in my freshman year of college." Take some time to tell your instructor about your honest opinion of your writing skills, and then explain what your overall experiences with writing have been. If writing is something that you hate doing and feel you are bad at, say so and explain why. Most people don't intentionally write something that they consider as bad, so explain why you think you are a bad writer. Chances are it has something to do with grades that you have been given in the past. For example, there was a time when I personally questioned whether or not my writing skills were as good as I thought they were. This doubtful period was triggered by my writing professor writing a single comment on my first paper. She wrote, "Pray for inspiration." The comment was hurtful, but I took it as a challenge and learned a lot in the following weeks about how to improve. Those are the kinds of things you want to explain to your teacher.