Might it be a sequence of chords (usually four) that can repeat in a loop with the guidance of a poster on my wall of the circle of fifths, or might it be an enticing drum beat from a sample, virtual drum machine, iPad, or talented friend. I find it partly a mystery and partly sitting down in the studio at regular hours prepared to work. Amazingly, something almost always springs forth that begs for a bass line or melody line. I understand that portion of the creative process because I have an experienced musical ear and harmony insight supported by humming or improvising on the keyboard. The skill of adding layers of arranged tracks comes more with experience. Great! Now the verse is done. Oh, no! How do I transition to the chorus or vice-versa? Circle of fifths. Experimentation. Try some samples. I'm trying to use standard song structure that has met the test of time. Even for a repetitive House or Techno track. To me, a song must take the listener somewhere. Finally, what appears to be something resembling a song, but in most cases, it's time to come up with lyrics. I loop the verse, pre-chorus, or chorus over and over again to discover what phrases come from my imagination. I might need help to find the rhyme to those phrases with rhyming references. Get some opinions from trusted musicians or friends. Listen to advice and feedback which may be painful because you may have to start the process all over again. If successful, you will want to write another song and --- start the process all over again! Good luck!