What do you like doing? What are you good at? Think about how you can make your interests into a project. Are there issues in your school or your community you would like to tackle? You may already be working on something or have accomplished a goal. In that case, base your proposal on that and take it to another level.
Read about Herbert Hoover to see how he was involved in all these areas and how he motivated others to help! (Making money is permissible)
Class projects are not eligible. If needed, enlist volunteers to help you accomplish your goal.
Note: You propose the project in your application. You don't do the project before applying.