I usually do some automatic writing to find a flow and then work on figuring out the voice. Those are the two most important parts of the writing for me. With other games it usually involves figuring out the mechanics first and finding a voice that fits that, but for more literary/lyric stuff it's all about flow and voice, and atmosphere as like a tertiary thing.
It's definitely something to practice because I have that same issue sometimes. But even then, just starting to write without a goal is a great place to start, even if the brain is being the brain haha
I'd also suggest setting a goal of like 2k words and making yourself fill that. Just write absolute nonsense, repeat the same word over and over again. Anything to tap into that flow state. Cause once you hit the flow, the brain can be involved and you can plot and structure and all that other stuff. The flow just helps reach a point where you aren't, like, stuck looking at the blank page wondering what to write.