I have never run a sound board, but I have suffered a lot of pain (literally) from sound systems, so let me tell you a little.

1. You need to run a "sound check" where you listen to the individual musicians and their mikes before really firing up the boilers.

2. Don't have wires piled in coils. They turn into generators or something and cause painful feedback.

3. If someone tells you the music is too loud, turn it down. Yes, there are half-deaf rock fans there who will tell you to ignore them, but what do they know?

4. Feedback also occurs when a microphone gets too close to some other part of the system, but I forget just how. Anyway, i was at a dance event where the caller kept wandering around and generating feedback with his personal mike. Finally we sat on his head. The pitiful thing was the place was so small he even didn't even need the darn microphone. It was just a status symbol.

5. If the audience is clustered at the opposite end of the room from the speakers, the sound is too loud.

6. Higher-pitched instruments carry more energy than lower, so be especially careful about the loudness of whistles, fiddles, etc.