How do you write a letter to the principal giving ideas to improve the school?

Well, you should be professional about your letter. I suggest typing the letter, have someone proof read it for spelling and grammatical errors. Make sure your ideas are actually going to improve the school and not just something that you want to be done. For example, the principal may not take your other suggestions seriously if you suggest that he make school a 4 day week as opposed to a five day week. Do not make the letter anonymous either, let the principal know who you are. Be sure and state why you think the suggestions you will be making would be a good idea and if they cost money you should suggest how your idea will be funded or if he should cut costs in a different area. Then either give it to him or to someone that works at your schools office and ask them to deliver your letter.