In the Beginning
In a pop song, no lyric may be more important than the opening line. You're not afforded the luxury of length as you are with a short story or novel, nor the grace of a courtesy look-ahead as with a poem. You often have to get to it quickly, and it better hook 'em.
There are a couple of ways to approach this, sometimes Eiger-like, task.
A serviceable go-to (particularly for a narrative-heavy song) is a well-written scene-setter:
"Busted flat in Baton Rouge, waitin' for a train"
"I was born by the river in a little tent"
"You get a shiver in the dark, it's a raining in the park but meantime"
For a more focused theme-oriented tune, there's the suspense builder:
"Looking through some photographs I found inside a drawer"
"Oh mmm I know a place"
"How come he don't come and PLP with me down at the meter no more?"
NOTE: "PLP stands for Public Leaning Post, old American slang for one person (usually female) leaning against another (usually male) in a friendly fashion." (the ol' Wikipedia)
And then, for songwriters that know exactly where it's all headed, there's the thesis statement:
"People are strange, when you're a stranger"
"The sweet pretty things are in bed now, of course"
"Now, I dialed 911 a long time ago"
Among many great entrances, my favorite might be Joni Mitchell's "No regrets, Coyote." It's a bit of all of the above, and it throws you right in with a defiant woman of her times, who knows who she is and is resigned to the costs of that. Knowing Mitchell's back story helps, but it's not necessary. When I first saw The Last Waltz at 14, I knew nothing and was still captivated when she launched into the line. Just like philosophy is a all just a footnote to Plato, the remainder of "Coyote" is all just a footnote to that first line. A great ride, particularly when she performs it with the Band, but a footnote none-the-less. Is that good or bad? I don't know. Ask Dickens.