We’ve already talked about the importance of structure to write a good song. There’s another very very simple rule you can follow to write a good song. It still concerns structure in some way, but doesn’t really have a name; I call it the Multiples of Four rule.
Music isn’t written as one really long stream of notes. It’s divided in chunks called bars (or measures). A bar groups a certain number of beats together; most pop music today sounds like 1-2-3-4 and is generally in 4/4. Without going too much into the theory of music, the point is that you need to be able to count the bar in order to identify how many bars there are before a change occurs in the song.
Spoiler alert: there is a change every 4, 8, 16, etc. bars (multiples of four!)