Formula or no formula?
Of course we all want to be on our "A" game every time we sit down to work on our hit songs. But what do you do on the days where you ain't got it? A purist might tell you that you need to wait on the muse to come around, or for the inspiration to strike. But there's a lot to be said for muscling through it. And one of the best ways to go about that is to come up with "songwriting assignments" for yourself.
For example, something I'll do is try to write a song based on a description of an album or artist I've never heard. You know, a new record will come out and there will be rave reviews in all the magazines where they say that the record sounds like so-and-so and that they've finally returned to their roots. Or maybe you've never even heard the artist before. I'll try to write a song solely based on these descriptions.
Neil Young used to write songs using titles like "Strawberry Fields Forever" that were already famous, just so he could knock those songs down to mortal level and place himself on the same playing field.
One of my favorite stories revolves around Def Leppard's "Pour Some Sugar on Me". Apparently, producer Rick Rubin loves giving out songwriting assignments. He encouraged Tom Petty to write a song based on the beat of the Def Leppard classic, and Petty came back with "It's Good to Be King". He did the same thing with Weezer singer Rivers Cuomo, who came back with "Beverly Hills". Here's Cuomo's take on it:
Rick [Rubin] actually gave me some assignments over the past couple years. Like he said, Write a Billy Joel or Elton John type of song, and I just took that to mean, write a song on the piano. And that was part of the inspiration for “Haunt You Every Day,” which closes the album. And he said, Write a song with the beat from “Pour Some Sugar on Me” by Def Leppard, and that was part of the inspiration for “Beverly Hills.” He told Tom Petty the same thing, and Tom Petty wrote “It’s Good To Be King.”
Actually the whole article is worth reading. Cuomo is has experimented with all kinds of writing styles, both formulaic and otherwise. Rolling Stone reports that he once kept a detailed database of all of his songs, as well as a three ring binder called "The Encyclopedia of Pop" in which he dissected Nirvana, Oasis and Green Day songs in the interest of cracking the code. The logic was that if he could figure out the formula to those bands, he could figure out his own formula and then have an endless supply of songs.
The bottom line is that there's no one way to write a song. And if you're not feeling it, there are other things you can do. Just keep moving forward, and you'll work around it.