From “The Essential Secrets of Songwriting” website:
When was the last time you heard an intro to a song that really captivated you? It never ceases to amaze me how mundane intros can be. So many songwriters spend countless hours on their melodies, chords and lyrics, and then when it’s time to get the whole thing together, they start by mindlessly strumming an irrelevant rhythm on one chord, and try to call it an intro!
An intro is crucial to drawing the listener in, and a way to make it sound like something great is about to happen. If you neglect this very important element of your song, you’re running the risk that potential listeners will simply click the “off” button and move on to something else before they even hear your song.
Intros are not peculiar to popular music; classical composers would typically start symphonies with an introduction, and we’d be wise to learn from them. In their case, the intro would introduce important rhythms and melodic fragments that will appear in the melodies to follow. It was a way to set up the mood, to entice the listener, and to keep them listening.
Your intros really need to do the same thing. They need to describe something of the song to follow. In short, an intro introduces the important elements of the song in such a way as to compel the listener to keep listening.
For each intro that you create, simply ask yourself, “Would I want to keep listening?”
I love using the Beatles’ music as a great model in this regard. Many of their songs didn’t even use an intro: “Penny Lane” and “Hello Goodbye” spring to mind. But the songs that do use an intro use really interestingly crafted ones: “Lucy in the Skies with Diamonds”, “Because”, “I am the Walrus”, etc.
All I’m suggesting is that if you’ve put so much thought and time into the main body of your song, why start it off with a monotonous and meaningless strumming of a guitar chord?