I sing in an oldies band and sometimes we gig doing acapella. Talk about putting yourself out-there!

The biggest advice I can give is to warm up before your gigs, practice your scales, practice your phrasing and breathing along with your phrasing.

I have noticed practice makes a HUGE difference in my singing. It purifies your voice, extends your range, and keeps you on key. I sing in the car to the radio all the time. I practice songs out of my range both HIGH's and LOW's and I'm starting to hit some of those notes which were once out of my range.

Hope that helps a bit.
Al