Capturing the Music
Relation to the band & purpose
This is the first thing to think about. Why are you there? Have you been invited by the band to take photos, but the venue? Or is it another reason? These questions will affect where you are able to stand, how much of a nuisance you can make of yourself, and how long you are able to shoot.
Location
Get there early. As early as you can. There are two reasons for this. Firstly it gives you the chance to scope out the stage and figure out where you will get good shots from. (assuming there isn't a Photographer pit at the front) and secondly, it gives you a chance to actually claim that location. Once you have a good spot, pay attention to the crowd. How busy is it getting? Whilst it is great to be able to move around and get images from lots of locations, in a small venue with a lot of people, trying that may get you stuck in a terrible location, or with a terrible view. Music fans won't have any sympathy for you.
Camera
Whatever camera you have is the one you have to use, learn to understand where everything is, and practice changing lenses in the dark. Unless you are lucky enough to have a camera with backlit settings (Like the Canon MkIII) then you will also need to get used to making changes to settings that can only be validated when looking through the eyepiece. Before your first gig, get some practice in, otherwise, you will be fumbling and turning the wrong things off!
If you are fortunate enough to have two bodies, this can be a big help, strap them both on with different lenses and you are able to much more easily get a selection of shots, and you can tailor the settings for that lens. When I had a Sony and a Konica it was a great help and it is something that I miss.
Lenses
I try and have three lenses available.
Prime: I use a 50mm prime, f/1.8 when I shoot gigs. It’s a great, fast and cheap lens. However, even at 1.8, the focusing can be tricky and it can be very easy to get a razor-sharp image of the microphone and a blurry singer.
Zoom: A decent zoom allows you to get a very close shot of a singer as they hit just the right note, or of a power cord being rocked out. The issue with a zoom is unless you have serious cash you'll be using an f/4, which can be a little slow when zoomed right in (as you all know, the longer the zoom the faster the shutter needs to go to ensure there is no shake visible; tiny movements transform to big focus changes)However, I tend to think outside the box here and use my 105mm f2.8 IS Macro lens. Whilst it is a macro, it is fast, stabilised, and 105mm on a MkIII is actually about 140mm which is generally good enough to get you a close shot.
Wide Angle: When you want to get the whole stage, if there is a big band on, then you are going to need at least one killer shot of all of them. To do that, you need a wide-angle lens. Please bear in mind I'm shooting with a 1.3 cropped sensor, so those of you with full frames could use a lens like the 24-105mm and get wide enough at the low end, whereas if you are using a 1.6 you will need to shoot with something closer to a fisheye! Comfortably sat in the middle, I am still to decide whether my f4 17-40mm or f4 IS 25-105mm is the better choice. With the 25-105mm I sacrifice width for IS giving me a little more speed.
Misc
Notebook: Bring a notebook to write down song names, band names, and anything else that comes up. It will be used.
Business Cards: Also, bring along some business cards, it’s quite likely if you aren't there at the invitation of the band and they are yet to make it big, that they may want copies.
Manual setting
Aperture
Unless you have an amazing lens like the 50mm f1.2 you will want to make your aperture as wide as you possibly can. get as much light into the sensor as possible to allow you to keep your ISO as low as you can. Basically, set your aperture to the lowest and forget about it for the rest of the evening.
Shutter speed
How fast can you handhold a steady shot? Make sure the shutter speed is that fast or faster. I find myself tweaking shutter speed and ISO a lot during a gig. The primary driver is keeping shutter speed fast enough to capture a sharp (or artistically blurred) image and set your ISO as low as that allows. Personally, I tend to shoot somewhere between 1/60th and 1/80th. Though these change with how zoomed in I am. With a 200mm zoom, 1/60th will not be fast enough.
ISO
As low as possible. Even though new cameras and software like Noise Ninja do amazing things at removing noise, you are better off not having to think about it at all.
Image Stablisation
If your lens has it, congratulations! That means your shutter speed can be a little slower, your ISO a little lower. IS is a wonderful thing.
Exposure
Try shooting a stop or so underexposed when you are doing a gig. Cameras struggle with the moving lighting, and it's easy to lose details.
Metering
A lot of photographers don't adjust this setting for some reason. It can make a huge difference. In the case of gigs, it depends on the venue and the lighting scheme, but experiment with changing the metering scheme from centre weighted to one of the others. I've had good luck when one person is on stage using spot metering. It gives you a little more control over what is considered average light.
Focusing
General automatic focusing struggles with gigs. Too slow, too inaccurate.
Knowledge
Note the band names as they perform, or take a photo of the playlist, It’s easy to get them mixed up after the fact.
Try not to shoot the roadies.....
Politeness
No matter why you are there or how, remember you are a guest and, unlike the people who have paid good money to be there, you are not there for the music, but it is only polite not to ruin the music for other people.
At a death metal concert, you are probably fine clicking away, no one is going to hear you. At an unplugged acoustic event, every click of your shutter may be an unwelcome annoyance to the fans and performers. If you are being disruptive, you are being rude. Sometimes you will just have to accept you are being rude, but be aware and do what you can to keep it minimal. If you want a better idea of this take a look at Joe Pug Live at the Relentless Garage