That's a great question.
I haven't done anything in public since the CV-19 thing.....but it seems as though you have experience performing, or at least you have some good thoughts about music at the keyboard.
I don't want to make a laundry list of things I personally do...it's kind of ritualistic in my case, involving loading in gear, checking my equipment (no that's not slang for anything), so that very little is left to chance when finally (after interminable delays and meet-and-greet "opportunities" and whatever) can play.
I am somewhat careful about diet and general sense of physical well-being before an important date, as well: that doesn't mean I won't have a beer or a glass of wine, but I'm assured that I won't have explosive diarrhea on stage, so that's one less thing to think about.
But, I do that generally before my day job as well, so it's just a general regimen I follow. It's not really wake up, do 100 press-ups, shave with a straight razor, and say ten Hail Marys, but there is a kind of method I like to follow.
More or less, I try to identify the sources of uncertainty and eliminate them, as much as possible.