After each tweak, smell the grounds dry, then after brewing, and finally the cup. A pass is when you get a clear, pleasant aroma—floral, fruity, chocolatey, whatever the bean promises. A fail is when it's still muted or smells off. If you've adjusted grind, time, ratio, and water temp and it's still lifeless, your beans might be stale, or your machine may need descaling. That's a separate issue.