Songwriting is art and craft. Most good writing of any type has a million revisions and tests in it from the author before it starts to sound reasonable. I have a written a few songs and they have always involved singing them over and over again to get the words right. It always helps to get something out that you can change and edit rather than keeping it all in waiing fo rthe perfect phrase to appear. A good book about writing that you might like to find and use is "Writing Down the Bones" by Natalie Goldberg. Sorry I'm rambling. I also find that different songs and topics seem to demand or require different structures. So you may find that as you write more that you are experimenting with alternate formats.