Well, that's what EN 121, EN 122, and EN 123 are about. Good papers accomplish their purposes. Think about your audience. Your teacher is almost always your audience, but sometimes the teacher designates other audiences for you to consider. In either case, remember that readers want to be interested and respected.
Good papers get through to their intended readers.
Use a moderate tone, unless you have strong reason otherwise. In general, write as a reasonable person writing to other reasonable people about something interesting. Good papers usually persuade readers that the writer is level-headed. Be as specific as your purpose allows. It is difficult to strike the right balance between general statements and detailed ones.