Clarity is one of the principles I learned from the great Stephen Sondheim. Lyrics written for the musical stage, he teaches, must be easy to understand, non-intellectual, concrete. That applies also to other song lyrics, especially to pop songs. What good musical songs additionally need is a subtext. There must be something between the lines, something that remains unsung, or else the audience may become bored after a few bars. It's important to let them sense another truth behind the words we hear. By far the best subtext is irony. It has three disadvantages though: Irony is difficult to write, hard to perform and rarely understood by the audience.