how will i write the manifesto
I assume you mean a manifesto declaring your vision and opinions on how to improve sports at your school.
You need to capture your audience and inspire them. If the majority of readers agree with your solutions and believe they can be implemented, this will go some way toward inspiring them. You must show that you have put a lot of thought into your manifesto by also pointing out what might go wrong and how you might resolve those problems.
It is also useful for you to explain who you are and why you are writing the manifesto.
1. Start by explaining who you are and what vision you have.
2. Explain how you are going to achieve your vision.
3. Explain what problems you anticipate and how you might solve them.