Might be useful to try and get a tripod, since you'll be zooming in (not IN the shot, but you wont be standing really close, so you'll have to zoom in before you take the shot, if you get what I mean) you're going to get some camera shake.
I've never filmed a band before, but I'm going to try and give you some advice, or babble about how I would do it.
On music videos and concerts these days, the camera guy really likes to get under the singer. Some of the angles are annoying, but have you noticed how the camera is pointing up - almost under the singers chin?
Don't stay on the singer too much. Since you have two cameras, you could work out something between you, for example you could take all the far away shots, or most of them, or whatever - and the other person could do most of the closer shots.
If the lead guitarist is having a solo, focus on him/her, and then maybe move to camera to see how the other band members are interacting. If the other members are standing still, then just stay on the guitarist. You don't want to hold the camera on the singer, if he or she is doing nothing. Same goes for anyone who's soloing, or looks particulary interesting.
You'll edit later, so make sure you have a good range of shots that show the WHOLE band, and some of it, then bits with just certain members. Remember to show the drummer at least once, depending on how close you are you can do some cool tricks with the camera. People often forget to give the drummer a moment of glory, so try and put him/her in. (no I'm not a drummer
)
I'll edit this if I think of something more interesting to say. Good luck!
-Chris
