If there was only one public speaking tip I could give everyone I've ever helped, it would be this one:
You need to kill your inner monologue when you walk on stage.
There. That's it. I guess I'm done, right?
Well, here's a bit more about it, in case you wanted to hear more.
I'm not saying verbal ticks or weird mannerisms, or poor preparation aren't big deals. But I don't think it's as big as how easily our inner monologue can push us off our game.