@joshmillard when I wrote songs in the past I often found myself repeating melodic or lyrical styles. I found that it's difficult for me to pick a theme and build around it (write something happy) but I could force myself to not slip into the same paths.
For example, constraining myself to use no minor chords meant that I had to user other musical techniques to explore what I wanted to write. Modulating/changing key or augmented/diminished/suspended chords gave new paths to walk. πΈπΆπ€