When I first started working in tv I used to film bands, partly for fun and partly as away to learn how to shoot and edit. I have filmed loads of bands over the years, from tiny concerts to large festivals and I always enjoy it. If you are new to filming I would defintely recommend it, there are always bands about who are desperate to have some kind of video and it is a good way for you to pick up some skills. Here are a few tips:
Get cameras. Music tends to but cut fairly quickly and you obviously need something to cut to, so the more cameras you can get the better. Get as many camera owning mates involved as you possibly can. If you can't get people to shoot, just get the cameras, even a locked off camera pointing at the stage is better than nothing. A few go pros attached with k clamps will give you another angle and help the edit along.
Learn the song. You'll be able to shoot a song better if you know it. Even just one listen will be enough to give you a feel of where a guitar solo might come, or when a backing vocalist might sing.
Shoot non-synch. This is hugely important. I have shot low budget music videos where we only had a couple of cameras for a live gig, the only way to deal with this is to shoot tones and tonnes of non synch. There are loads of ways to do this, you could shoot the band back stage, getting ready, travelling to the venue etc and cut it over the live performance. Another option is to shoot lots of crowd cutaways. You can also just shoot lots of non synch of the band playing, for example you can shoot close ups of anyone not singing, or shoot weird angles from behind the band so you can't see what they are playing. All of these shots can then be cut in with your actual live footage. Another option, to make it look like you have more cameras on the actual performance, is to get the band to do a run through before the gig starts. If they are playing to a click track, the shots will cut in perfectly to the live performance, if not you will have to fiddle around a bit in post, but it does work, bands tend to be pretty acurate when they are playing and the tempo will probably match. The only thing to be cautious of with this route is continuity. Make sure the band all know not to change clothes between the rehersal and the gig. The lighting will also need to be the same.
Jam synch. Lock all your camera's timecode together for the actual shoot. If your cameras don't all have this function, then at least role for the entirity of which ever songs you are using for the edit, so that the songs can be easily locked together in post.
Audio. Get a decent recording of the music. The easiest way is to take a feed out of the desk and put it into one of the cameras that won't be moving.
Here is a performance from Rudamental at V festival which I shot over the summer. There were quite a few cameras on the actual performance, but there is also loads of non synch of the audience, which was shot before hand. There were also a couple of go pros mounted just over the stage, which I think worked really well.