I'm no expert, but I have recently done some gig photography for a local band playing in pub venues and learnt a few things.
From my experience the 50mm f1.8 is your friend and prime workhorse.
White balance, take a piece of white card and set the balance under the stage lighting. I was lucky enough to be able to get this done before the band started. This allowed me to get proper skin tones and light colour.
Ask if there are any particular shots they want. Hopefully the band will be happy for you to get in amongst them so you can get some good close-ups. I don't know what venue they are in, but background can be a pain in small places so close-ups could be the best option. Flash can also work well, but not everyone likes flashguns popping in their face