Small gigs of big gigs? Entirely different worlds.
Learn to focus manually
Ear plugs, get them or get deaf. You'll often find yourself very close to PA speakers at smaller gigs. You'll loose your hearing quicker than a drummer, I'm not joking.
Never ever ever ever ever ever ever use flash! though very small gigs with crappy lighting, maybe... it just kills the atmosphere for the paying punters and ****es off bands. Though plenty do it, I won't.
You need fast glass. 2.8 is a minimum, get faster primes over zooms if you can afford it.
Don't sign the copyright robbing contracts to shoot the gigs, ever. Have the balls to walk away.
Get insurance, often does a drunk punter see a nice camera and grab it. Or you get a whole load of beer over your gear, yay, love that one.
Learn to use manual mode properly, use partial/spot metering. Thanks to digital, you'll know what you're doing in no time here.
Learn to focus manually
If you're in a pit, be nice to the other photographers, don't hog a single place for the entire gig, share the love. Plenty don't, don't let another photographer ruin a shot and get in your way.
If you're not in the pit and in the crowd, prepare for cracked ribs. I'm not joking, I've seen it more than once. Only really something to be wary of at metal gigs though. Though Justin Bieber fans are a bit mental...
... Learn to focus manually...
Gig security can be a pain in the back side, but do not get too arsey with them. If it seems like they won't budge, just be nice and do as they say. If you shoot regularly you'll seem the same people time and time again, and they will remember you and make your life hell if they don't like you.
Mostly, enjoy shooting. Music photography is one heck of a challenge, no better way to sharpen your skills.
Can't believe I've put this much effort into a 4 word question...
Oh and hey, guess what? learn to focus manually!