Whenever I'm working on one of my songs I'm often reminded of the way Ray Davies of the Kinks described his first major hit, "You Really Got Me." On more than one occasion he has likened the structure of "You Really Got Me" to the way someone tries to "chat up" a woman (or man) in a club or bar.
What did the head Kink mean by that? Well, simply put, when it comes to pop music, you quite often only have two or three minutes (if you're lucky!) to make a good impression on the listener, and you damn well better have a GREAT opening line.
That is exactly what "You Really Got Me" has - a punchy opening riff that demands your attention and makes you curious about what's coming next! Think of it as meeting an attractive member of the opposite sex and starting off with a great joke. You wouldn't launch into a long, rambling tale about where you grew up and how your parents didn't love you enough. That would be crazy!
There will be plenty of time for deep stories LATER if everything goes well. The same goes for songwriting, metaphorically speaking. If you have a song with a long, moody two-minute intro that you passionately feel needs to be heard, you can put it on your first full-length effort, because whoever's listening is probably already interested in what you have to say. (Just like your wife has to listen to all your ceaseless rambling about bullsh*t like your boss at work. She's trapped!)
However, when you're a relative unknown, you want to grab people's attention quick and give them a reason to STICK AROUND for the deeper stuff. And none of this is meant to suggest your "opening line" has to be goofy, shallow, slick, or stupid. There are many simple, direct jokes (and many simple, direct musical hooks) which belie their depth and hint at greater complexity to come. That's the type of opening salvo you want to strive for: something that "really gets" the listener going and hungry for more.
But you gotta get someone's attention first.