I used to get nervous, but then I did a run of gigs one summer with a singist who would just add to the set list willy nilly. “Oh, let’s play (insert random song title here), it’s really easy” mid-set! The guitarist was a song encyclopaedia, so we’d count in and I’d try my best not to look like a completely useless tw@t. Hell of a learning curve, but my nerves are no more!