The key to taking good concert photos is understanding how exposure metering works. A concert stage is a nightmare for a camera exposure meter. You usually have a very dark background, with the subjects you're trying to photograph brightly lit, often with coloured lights that can quickly vary in brightness. Add to this the fact that despite all the apparently bright lights, the actual overall light level is actually quite low, and the subject is probably going to move around quite fast, and you can see that your camera's automatic systems are going to find it hard to cope. In this situation the best option is to take over and set your camera up manually.
One automatic system that is helpful however is image stabilisation. Some IS systems allow stable hand-held photography at very slow shutter speeds, and if you have a steady hand you may get away with exposure times of 1/10th of a second.
To prepare your camera, manually set the ISO speed to the highest level at which you're happy with the picture quality. On most modern cameras the quality at 400 ISO is quite acceptable, but some high-spec bridge cameras and DSLRs can produce usable photos at 1600 ISO with no problem. Setting a higher ISO value means that you can use faster shutter speeds, reducing the problem of motion blur.
Next, manually set your aperture to its widest setting, in other words the lowest f-number. On most compact cameras this is going to be in the order of f/3.5, while a top quality DSLR zoom lens might got to f/2.8. This will drastically reduce the depth of field, so you'll have to be precise with your focusing especially at close range, however the blurred background effect that this produces can look great for this type of shot.
As for shutter speed, this will depend on the lighting level of the concert. A full festival light show is obviously going to be brighter than the back room at your local pub, so you'll have to experiment. Unfortunately it's impossible to tell in advance, you'll have to wait until the concert is under way to see what you can get away with.
Metering the lightshow is tricky, but not impossible. As I explained in the link at the top of the page, you camera's light meter makes certain assumptions about the scene it is measuring, and you can use these to your advantage. The easiest method is to set your camera to aperture priority, set maximum aperture and zoom or our in until you have a large area of the stage in the frame, but try to avoid having any of the stage lights shining directly into the camera. Half-press the shutter to take a light reading, and note what shutter speed it recommends. For an average gig it's probably going to be something horrible like half a second or even longer, but don't worry, this is just a starting figure. The light meter is suggesting an exposure setting to make the whole scene grey, but in fact most of the scene should be black, with just the lit highlights visible. To do this, take the shutter speed that the meter suggests, and increase it by four or five stops. So, if your light meter suggests half a second, switch to manual exposure and set the shutter speed to 1/30th of a second. The big advantage of digital cameras is that you can check right away to see if you've got it right. You may need to adjust the shutter speed up or down a couple of stops, but you should find a value that works for the current lighting. A slight under-exposure is ok, because you can always adjust it afterwards using editing software.
Focusing can be more of a problem. A lot of compact camera autofocus systems don't work well in the dark, especially with moving subjects, and even more so at longer zoom ranges. Again DSLRs are much better at this sort of thing, but if your camera just can't hack it, then try switching to manual focusing if it is available. A good trick is to initially focus on the singer's microphone stand, which is usually highly visible, and then make small adjustments from there. An optical viewfinder is a big advantage in this situation.