In my experience, every piece you write makes you feel like a new composer again. That’s because every aspect of writing a piece comes with limitations and guides you in specific directions. They all make demands on your writing that require you to become a new composer.
The text makes demands. The commissioning ensemble makes demands. Your state of mind comes makes demands. The melody that joins the text makes demands about the harmonic language and formal structure.
Everything you learned about your writing from the last piece might be utterly useless with your next piece. All you can do is to recognize that you are a new composer again, and put pencil to paper.
(And recognize that being a new composer again might unearth very old experiences from life. One project I’m working on right now asks me to integrate my love of Lewis Carroll, Baroque puzzle canons, auditory illusions, and the foundational work from Douglas Hofstadter, Gödel, Escher, Bach. I know that nothing I’ve written before has much bearing on this composition, and I also know that I’m unlikely to require the specific knowledge I’ll develop while writing this piece.)