When learning a new tune I do something called "burnishing". I learned of it from a magazine interview with Christopher Parkening. He suggested practising slowly and applying more pressure with your fretting hand than you would while performing. This really gets the positions and notes in your memory and builds strength in the fretting hand.
To kind of reiterate what Allan C said above I think it's really important to also entertain yourself while performing. Don't be so intent on pleasing the crowd that your not listening to what you're playing and singing. Allow yourself to be moved.
Great thread Rick.

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