"Patience in Songwriting"
Patience is said to be a virtue. I don't delve into the theological realm, but I can tell you that for a songwriter, patience is an essential quality to cultivate.
I've harped (or at least I feel I've been harping) on not stopping writing until the song is truly done. Similarly, don't force yourself to finish a song when neither it nor you is ready. Sometimes, completing a song can take multiple sessions, weeks, months or even years. Despite my constant nagging on the topic, I keep hearing songs that lack polish, that have obviously not been edited, that are based on ideas that are only partially developed, or that have very obvious problems--usually of the lyrical variety.
Don't feel like you HAVE to finish the song in one sitting. In fact, my songs and those of my most successful songwriting friends are almost never completed in one sitting. With perhaps one or two exceptions (and I can't actually even think of those at the moment), I haven't finished a song in one writing session in the last five years.
In fact, I not only keep writing, I frequently play the song out (that is, perform it in public) before I consider it finished. Something about the energy of performing it for strangers really helps me find any remaining rough edges or any parts that just don't quite fit right or gaps that need to be filled in. I don't give too much weight to the public response (this is not a very sophisticated or friendly original music market), but I do listen to my own voice and ask "Do I really believe what I'm singing?"
"There" is a song I wrote with Josh Osborne and Tom Gould in two sessions more than eight months apart. In the months between the two sessions, it sat stagnant, to the point that as the date for the second session approached, I was certain that we would have forgotten all we had done the first time. Looking back now, I wouldn't have changed a single thing about the "process" of writing that song. Had I impatiently forced it out prior to being able to reconvene with Tom and Josh, I'm certain it wouldn't be the song it is.
Don't let yourself or your audience fossilize your song in a particular form, just because that's the way you first played it. Steve Earle never feels a song is finished. Steve frequently plays an updated version of a song he originally wrote in 1996, "Christmastime in Washington," with new verses and other changes. I also have heard him perform songs he first recorded in the 1980's with entire new verses, changes to the choruses and the like. If a song becomes part of your life, there is no reason why you can't continue to let it grow and live and change for years.
Even when you have a great idea or particularly powerful inspiration, don't force things. Capture all you can of your lyrical and musical ideas without trying to force them into a "song" structure. Then, when the flow from the muse-spigot starts to slow, begin to shape it a little. But don't feel like you are finished or have to finish it at that point. I find that I have to play the new proto-song over and over again, sometimes for days, fixing and adding and subtracting and shuffling and tweaking once in awhile.
Trust the song. Let it happen at its pace, not yours.