"I get nervous sometimes and not others. I have no idea why - there's no logic to it."

Yes, I'm sure that's true for all of us, to some extent. What all these tricks (see above) help to do is to reduce the incidence and severity of the nerves.

Sometimes a little bit of honest self assessment after a nervous gig will throw up some insight. Like "perhaps starting with the difficult instrumental wasn't such a good idea". Often I look back and ask myself why I put myself under unnecessary pressure. Although it's good to stretch one's bounds, there are times and places...