My trick back when I wrote songs of my own was spontaneity. Expose yourself to enough media and eventually, much like how an AI works, you'll start getting ideas of your own based on the material you've consumed. It happens at pure random, at any time, anywhere. Usually when it does you have about half an hour to get it done. The spontaneous material is usually FAR better than anything you could force yourself to write. I've put together some things I'm really proud of this way. The downside is that the spark goes eventually and there's no telling when it'll come back. I haven't written in a year, but when I was fifteen I cracked out two dozen songs in a few months.