I will assume you are a student, or possibly a parent. Regardless, it is exciting to hear that you are invested in the school and seeking to make positive change.
I will give general advice and then add some specific suggestions for a student vs. a parent.
First, I would use a word doc (or equivalent) to compose a letter that is formal - Dear Principal ___ - including a date and the clear name and address of the school.
Next, describe who you are and your connection to the school. This is helpful context, and (likely) establishes you as an important “stakeholder.”
Then, describe your specific experiences, or observations within the school, which have probably led you to conclude that there are problems in need of improvements.
*This is very important* Before you describe possible changes, share in detail what you’ve been through or seen; this will add weight and credibility to your letter.
Then, offer to meet with the Principal “to discuss the concerns you raise and possible solutions for improvement” - this allows for you to learn (a) what the Principal already knows, (b) what steps they may be taking already, and (c) gives them space to add input and shows your willingness to listen, rather than demand.
Lastly, you can say “to help with the process, I’ve thought up several possible solutions for improvement, and I would appreciate your feedback.”
By framing your solutions as example options for consideration, you invite yourself to be at the center of a process for change, rather than delivering an ultimatum that will lead immediately to conflict. Have a good day