From the point of view of the IELTS examiner: Functions of language: You would need to show that you can express an opinion and justify your opinion, or in other words, say what you would would like, and then go on to give reasons why you would like this. Grammar: You would need to show that you can use conditional forms correctly If I were a student answering this question, I'd choose a trip abroad as the prize. There'd be plenty to say about that, wouldn't there? Have a go, and write your essay in the Notebook.

Chris basically said it all, but it might be helpful to remember that though "prize" usually means something that you are awarded for winning something, it can also mean more generally something that you achieve for succeeding. These are both types of prizes: 1) The 1st-place trophy a runner wins at a race 2) The knowledge of a language that a non-native speaker gains after study While the first of these is usually the kind of thing that people mean when they say "prize," taking advantage of the second meaning I think might help you answer the question more easily. (Let me know if that was unclear!)

Thanks for posting this Skye Wang. Think of something you really want! Now think of how that thing would change your life. Now think of what you would do to get that thing. This is a topic based solely around personal preference. If you ever need additional help you can find me here http://www.italki.com/teacher/1610322! Have a great day! -Chris