1) Be interactive with the audience - no matter how good ur speech is, it'll be outshined by others if you don't interact with the audience
2) Mention some of your qualifications - Why should they vote for you? What makes you more eligible than other candidates? Do you have any past experiences?
3) What do you plan to do for the student body and school? - Make it realistic, and keep it simple. This is perhaps the most crucial part of your speech
4) Try to make yourself relatable - Crack a few jokes if you can, and attempt to reach the people (for example, you could say something along the lines of, "I'm a student too, so I know exactly what we all need and want..." etc.)
5) 200 words means you need to create an effective, concise speech. Brainstorm your speech first.
6) If you can, add a famous quote. Definitely create a unique statement everyone will remember. For example, "A vote for X is a vote for hope and change!" etc. The more relatable, funny and interesting you are, the more ppl will remember you and the more inclined they will be to vote for you.
Hope this helps!