What are some small, almost negligible routine tricks that actually impose significant change to your aim?

One of those things for me was washing my hand with soap, especially the palmside of my wrist. It really, really helped my mouse grip and drastically reduced friction against the mousepad cloth because of my naturally oily skin. I do this before every match, and play better than when I often forget to. Another thing is taking deep, consecutive breaths at the start of every round, and swaying the crosshair whenever I peak a corner to help retain focus despite my undiagnosed but possibly apparent ADHD.