The setting, The main character, The theme, The problem and solution. The begining, middle or end. And lastly the POV (point of view)
A polite person may always say thank you and please. They may hold open a door for someone. They are always courteous to others. Polite means caring about others and showing respect.
You would need to spend the most time on the introduction because its where your readers know what you are talking about. If your introduction isn't clear, the rest of the writing wouldn't make sense to the reader.