Are there rules to writing a song?

Use a consistent progression of keys and chords. The information, the story and the details are in the verses. The pre-chorus increases tension and makes you want to hear the chorus. I'll write a full article on this idea with some solid examples to make more sense, but for now, start taking a look at your favorite songs and see if they're doing it.

The structure of the songs is important if you are a composer, but what I have discovered is that there is no singular way to structure a song if you want it to be a hit.