Another one of my favorite advice which I heard from Josh Waitzkin is, "Don't forget the space you leave behind".
rust in je geest / rest in your mind
Never give up do not look at opponent rating.
Always use your brain, otherwise you will lose. I have not done this many times, and lost.
Stop playing that godforsaken game!! circa 1990ish
Also, good point mentioned above. I try not to see my opponents rating before I play. I wish TD's wouldn't keep putting them next to all the names on the pairing charts.
Don't underestimate the endgame knowledge (or the speed) of 10 year old chess players. Been there. Done that.
Ignore Bobby Fischers non-chess expertise.
Don't quit your day job.