Jamie Zawinski, who owns San Francisco's DNA lounge, has some practical advice for people trying to shoot photos in dark venues, bars and clubs. In addition to tips on composition and lenses, he's got a lot of good solid stuff on bar etiquette:
Stop standing still.Nightclub photography: you're doing it wrong.
We know your photos are the most important thing in the world, but you're pissing off all the other customers by blocking their view with the enormous piece of gear you keep holding up. Especially if you're tall. Or have a ridiculous hat. Move around! Don't stand in any one spot for more than a minute. You will get a wider variety of photos, and you won't irritate the people whose view you're blocking if you weren't there long.
Also, keep your elbows tucked in. You don't have to hold your camera like you're impersonating a windmill. The less space you take up, the fewer people you will piss off.
Don't post photos where people look like crap.
This really should be obvious, but if a photo is unflattering or otherwise no good -- if the subject is making a stupid face, or the lighting accents their zits or whatever -- don't post it. Why do that to people? You're not Diane Arbus. Some photographers think "but people want to see pictures of themselves, so if I took it, I should post it!" but that's not actually true. For candid nightlife shots, people only want to see good pictures of themselves. If you don't have a good picture of them, you'll just make them feel bad.
Lose the giant watermark.
If you feel you must caption your photos, just put your name or URL at the bottom in a relatively small font. Especially do not use a huge transparent logo. It looks terrible and amateurish and it is distracting.
In my experience, the size of the watermark is inversely proportional to the quality of the photo.
Personally, I never watermark any of my photos, because it's not like anyone's going to go and get rich off of some candid shot I took of them in a club. I know other people are much more hung up on getting credit about such things, but try to be a little understated about it so that your desire for credit doesn't take a big steaming dump on the composition of the photograph itself!
(Image: JWZ: The Sounds)