RaMed Studios suggest when attempting to write a song its best to start with a title. After creating a title, create a list of questions from the title and then try to make some kind of structure in how you want to write the song. For example: how many verses and how many choruses.
Try asking the questions in your verses and answering them in your choruses. RaMed also suggests that you work on your melody at this point after which you will work on creating a bridge to bring about a resolution to your passage. The melody of the bridge should be different from the verses and choruses to create a nice contrast.