First and foremost, if you havent used an SLR (digital or manual), it's time that you familiarise yourself with one. They are the ones that take better photos in this type of photographic field. They are also the industry standard camera. There are plenty of places that you can learn about SLRs - try your local camera shop for advice, do a short course/uni degree (degrees usually last around 3 years, I did one of these), or read some books from the library. Above all, just practice and it will all come in time!
The way that I recommed starting out in taking live photos, is by getting familiar with the camera that you intend on using as your main camera for this type of photography. It is better to know all the functions and bits and pieces of your camera than not knowing what to do when something happens to it while at a gig.
LENS
The best all purpose lens is a 50mm one, preferably with a fast aperture/shutter speed on it. Anything in the vacinity of f1.8 to f2.4 is a fast lens. Mine is a Canon 50mm f1.8 lens, and it works extemely well in the tough lighting conditions. It was a fairly cheap lens (about $150), but if you are really serious about this type of photography, you can spend up to around $1000 or so getting an extremely fast lens. Later, you may want to get a zoom lens, but I have found that most zoom lenses get a bit pricey when you want a fast shutter speed.
FILTERS
I also recommend getting a 80b filter that attaches to the front of your lens. This is a deep blue colour and it helps eliminate funny colours, like that orange colour when you use daylight film indoors at night. It is around $25 for this filter (depending on where you buy it, and if you can get a student discount), and doubles as a protectant for the actual lens glass. It is also recommended that you get either a UV or skylight lens - this protects that camera lens even better than the 80b filter, and doesnt interfere with the cameras light diffusion.
FILM
The type of film that I usually use is FujiPress 800. It is around $11 a roll, and produces excellent results and colours. The reason for the high price? It is a professional film. You can buy 5 rolls for around $44, and get it even cheaper if you have a student card. Buy in bulk as it saves you money!!! You can also buy FujiPress 1600, it is a faster film and also used for this type of photography. Generally, the higher the number, the faster the speed of the film. In the past, higher speed film has been "grainy" in low light conditions, but the films that they have today are incredibly advanced in their emulsion coating, so never fear...you won't have dreaded grainy pictures! (Though you may get a few every now and again)
GETTING PERMISSION
Now that you have the equipment, the next step is to actually get the photos. And usually this is the hardest bit. Most venues will not allow people to take photos with SLRs unless they have a photo pass. And besides, you don't really get good shots if you are behind a barrier. Having said that, there are some venues that are pretty relaxed about the whole photography thing. Some examples are Newtown RSL (now known as @Newtown), the Manning Bar at Sydney Uni, Manly Fishos, Bar Broadway, the Annandale Hotel and some of the smaller venues. A general rule is that the smaller the venue, the more likely you are able to get in with a camera. Bigger or higher profile venues, will allow small snapshot cameras in, but not SLRs. Another rule is that the higher the profile the band, the less likely you are to get an SLR in. (Unless of course, you hide it. I've actually been able to sneak in a camera a couple of times. I've put the camera at the bottom of my bag with lens and body separate and then covered with black velvet.)
Now to getting permission, and getting in front of that barrier. Usually you will have to have a photo pass. These are usually given out to magazines and street press. So unless you work for a magazine or newspaper covering the gig, you won't be able to get in front of the barrier. You could try and ask permission(or even ask for a photo pass) from a band's manager (this has worked for me on some occassions) or try the record company, but it is usually really difficult. When you actually do get a photo pass, you will (in most cases) have to sign a release form for the band stating that the photos will only be used for the particular story that is being published for that magazine. This covers both you and the artist if someone else writes something bad or puts you photo in an article that you did not give it permission to be placed with.
Another option, in Australia, is to contribute to online music communities, like Faster Louder (fasterlouder.com.au). They send regular emails out with details of upcoming gigs for local and international acts with opportunities to take photos. To be selected for a certain show (especially for an international act), you need to send a link to previous photos, and will need to upload photos taken at the show within a 4 to 5 day period following the show. But it is a wonderful opportunity to get experience.
Now, say you have a photo pass. When you are at the venue, try determine the lighting conditions before the band starts. That way you will know what type of colours and images your camera will produce. You will also be fighting for position with a few other photographers. If the band is an overseas act, or a popular local act, there will usually be on average around 4 to 5 photographers at any one time (Example: Pacifier/Shihad are an extremely popular Australian/New Zealand act and have recently released their new album. A few of years ago, they played at the Metro Theatre in Sydney, it was their last gig before they were to record their new album. Due to the popularity of the band, the gig sold out and there were heaps of photographers. This band did not play another gig for two years - until the Big Day Out in 2002. Therefore, plently of magazines wanted images of the band before they were out of the public eye - leading to about 7 or 8 photographers crammed into a narrow area in front of the stage). You are usually given the 3 song rule. This means that you have 3 songs to take photos and then you have to leave the area in front of the barrier. This is the standard time for most gigs.
EXTRA TIPS
A few extra bits and pieces. I have been told that you shouldn't use a flash, as this usually "blinds" the performer for a few seconds, and may make them lose their place in the song etc. If a flash is really necessary, make sure that you have some sort of diffuser covering it - either a specially made diffusion cap or even a tissue. But if there are strobe lights being used, it's usually ok if you use a flash, they are getting blinded anyway!!!
Another tip is that you should wear black. This is so that you don't attract attention to yourself, and so that the performer doesn't feel that he/she is being stared at.
Also, don't get too enthusiastic and snap happy. Unless you have a digital SLR (not the cheapest things in the world...around $5000 for a pro camera. Although these days with the popularity of digital cameras, you can get a decent 6 megapixel digital SLR for around $2000 to $2500, like the Canon EOS 300D or Nikon D70...as with all things, try before you buy), you won't be able to go back and reshoot any images. I made this mistake before, and wasted alot of film and shots that were total rubbish. It is better to get the correct shot and framing, than just snapping away.
Another thing, do not take the stock standard shots of bands. Try something a little different and the image will standard out. Try different colours or framing, and don't always focus on the lead singer...there are other members in the band as well!!!
And one final tip. If your camera emits any sort of light, from either a light meter or an LCD panel, cover it up. It will attract attention to yourself, and you want the performer to be as natural as possible in your photos. Cover it up with something like black gaffa tape or cardboard and black tape.
These are some basic rules and guidelines that I have learnt while trying my hand at Live music photography...but my most important rule is to have fun (I've seen one photographer dancing away inbetween taking photos)...it will be alot better if the band that you are taking shots of is one of your faves, and it won't be as boring!!!