What I find really helps that nobody ever made clear to me.

1. Nerves and nervous energy are still energy. Think of it as a natural source of energy to help you do your best. I believe if you don't get a butterfly or two you've lost a spark from your performance!

2. You are good enough, personally. If you have really entertained 3 people who were objective you have all the talent and material to entertain some more. REMEMBER they have not seen you before and will not be as familiar with your material, and previous highs or lows. Don't educate them in your mistakes by apologizing or stopping: empathize with your audience, press on and look for the next high.

3. If you were really, really not prepared you would not be on the edge of this stage. That goes back to objective people in comment #2. REMEMBER preparedness is always a relative thing. You _are_ less prepared than (INSERT HERO HERE) but that's OK, he/she would never play this dump, is dead now, and isn't on the menu. :) You and the audience are lucky to have each other cause otherwise the show has a whole lot of nothing.

Lastly,

4. The audience is never wrong on their time. They may be stupid, uneducated, hate folk, or some other choice -- they are never wrong on their time. But YOU can choose your material and audience. If aisle c isn't happy finish your song for the sake of aisle d. Especially in smaller gigs get a sense of what they want to hear. You can't get this sort of experience without an audience and it will help you in your next gig. Don't hate jerks encourage and seek people who really enjoy what you do.

Be professional, finish your set, in whatever recipe for the night you choose -- shorter, longer, bawdier, faster etc... Thank the audience for their time and get ready to do it again armed with what you've learned :)