You have done everything right. You put together and tested your gear, making sure your batteries are fresh and your cables are in fine working order. Your strings are fresh and your guitar is relatively in tune. You know what goes where, so when your name is called your ready to play in a moment’s notice.
Usually the first thing that happens after a song is written is the recording of what is known as the work tape. This was usually done on a handheld recorder, but now is more commonly recorded on a cell phone or computer. It consists of the writer or writers playing their instruments and the melody being sung and perhaps a harmony vocal.