long sound checks are REQUIRED if you want to learn how to set up your sound. I suggest doing it on the afternoon of the gig ... spend time, mix the sound, listen on stage, have a band member or a trusted friend listen from the room. get the balance. Try severl songs or parts of sings. Get to konw your equip, and your set-up.

Then as time goesd by, you'll learn about speaker placement, monitors (if you use 'em) and pre-set volume, tones. Keeping levels low, as someone said ealier is very big help! I would plant trusted ears in the audience during the show and have them dicreetly comment as the show progresses. People come and go in the audience, the sound changes.

ALL instruments should be using pick-ups, if possible. On-stage; microphones are the enemy!!! They pick-up junk noise, not inetended to be part of the music, they feedback, etc ... use pick-ups. Fishman and Pick-up the World(look at them first) make the best products, that I am aware of, and both are reasonably priced.

Sound IS a very important part of your success as a musician. There are lots of ways to success, but ignoring the importance of the sound is NOT one of them! Learn how to use the equipment, or find a good sound man. It is nearly important as any other instrument. You can be great players, but if your sound is not under control, your audience will never know it!