Listen more than you speak, always step into someone else's shoes for but a moment, and embrace that tension because it will facilitate fundamentally better design work which makes stronger products.
Perfect is the enemy of done
Move quickly, build, and test solutions for specific problems iteratively, collaboratively, and in the shortest amount of time. Generally, ship it faster than you think you should — but not so fast that you're compromising on craft and quality. (Voltaire would agree with most of this.)
Get out of your own way
One of my biggest pet peeves is when someone says, "I can't draw." Because, unless there's some kind of physical limitation, the reality is that anyone can. "I can't draw" is an excuse because they think they should be better at it than they are. Let it go and don't listen to those inner Statlers and Waldorfs.
One last note, I’m a proponent of using the right tool for the job — not just what you’re comfortable with as a designer. Stretch, reach, and try something different. These days, I use:
Notion for creating team notes and wikis
Figma for creating pixel-perfect mockups, simple prototyping (though not quite Principle), and solid versioning — Sketch also has its strengths, especially in its wealth of third party plugins; and I think Adobe XD is breaking new ground
Keynote for making decks
Zeplin for design specs, assets, and code snippets
Magnet to organize my laptop workspace
Contrast to check WCAG 2.0 accessibility standards