Instead of a topic, start with an emotion. Name what you feel — and write from that feeling, not from a thought.
Close your eyes. Name one emotion you feel right now. Not 'I'm sad' — but what does it feel like in the body?
Thoughts lie — emotions don't. When you write from emotion, the text is authentic.
Instead of 'I'll write a breakup song' start with 'there's a stone in my stomach.'