First, a word of caution: while nobody is likely to mind you taking a few snaps of a local band playing a Friday night down at the pub, some large events at major venues may place restrictions on photography. Many digital cameras are capable of recording video and fairly high quality sound, so you may find that they are banned from the venue to prevent piracy and bootlegging. If you've got any doubts it's a good idea to ask first rather than risk being thrown out of the gig, and possibly having your camera confiscated.
On the plus side, if you contact the venue or the band in advance, you may find that they will be only too happy to have you take photos, and may even have a special area set aside for photography. If you are a reasonably experienced photographer and you're certain you can get some good photos, you may find that the band or the venue will offer to buy any that they like. However if you plan to sell your photos to other people, such as music magazines or the local newspaper, it is absolutely vital that you obtain permission from whoever is running the event.
Some venues may let you take photos from backstage or from the wings, but while you can get some good shots from this angle, stage shows are set up and lit to be viewed from the front, and that is where the performers are going to be directing their attention most of the time. The best place for concert photography is in front of the stage. At most larger events there will be a fenced-off area between the first row of the audience and the front of the stage, usually patrolled by concert security personnel. See if you can get permission to photograph from this area, because it gives you the best view, and you'll have plenty of room to move around.
Another good place to stand is right at the back of the audience, preferably on some raised platform. At larger gigs there will usually be a sound and lighting control platform positioned directly in front of the stage towards the back of the audience area. This is another excellent place from which to take photos, but make sure you obtain permission first, and always stand where they tell you to. An stressed-out sound engineer is a lot more dangerous than a concert security guard, so if they tell you to move don't argue.
If none of these places are available, then try to stand off to one side of the audience, as close to the stage as possible, but out of the way of anyone who may want to dance. You really don't want to get caught in a mosh pit with two grand's worth of camera tied around your neck. Don't take all your photos from one place though. You may find that you can dash from one side of the audience to the other between songs.
Unless you have permission and can set up in a safe area, it's very unlikely that you will be able to use a tripod, and it would be best not to try. You can pretty much guarantee that a drunk dancer will trip over it in the dark, and that really isn't going to end well. However you may be able to get away with using a monopod, since they take up a lot less room and are easier to move about. If you can use one then do so, because even a little support is better than none at all.