"You need to be about 30% better than you think you will need to be to do as well as you should."

That's really good advice.

On reflection I think a lot of what I'm struggling with is those extraneous things, like starting a number, realising your instrument isn't quite in tune and you've got a whole song to get through like that. Or like a talkative audience. It's things like that that make a gig trying.