我觉得你可以这样：①你想成为什么样的人,②这样的人未来会做些什么样的事（最好是积极向上的那种）,③最后填上几句对自己的美好祝愿,如希望梦想成真之类的,应该就可以了.
我附上我自己写的短篇给你：
Nowadays,there are so many people dying of cancer or some other diseases.So in the future,I want to be a doctor.I will firstly apply for a job in a hospital.I will do some easy task,such as the assistant for a doctor.Then I will do the surgery for the patients by myself.After accumulating some experience,I will take part in the research group and study more about cancer.Maybe I could find a way or more to kill some kinds of cancer.With my help,a lot of patients who now suffer from cancer could in the future become healthy again.
What's more,I will study really hard,so I could achieve my dream in the future.