I’ve been shooting events. No real surprise there as the only events I prefer not to shoot are weddings (I prefer to select people I am going to shoot, without the added pressure of a “mostly” once in a lifetime affair, but I will work as a second shooter for my wife). When preparing to shoot an event, there are many things to consider:
Venue – These range from huge outdoor areas to cramped rooms packed tightly with people. Many don’t allow flash. Some require all people that have “pro gear” (more often than not pro gear is a camera with a big lens on it) to either be registered or have a media pass.
Lighting – Light changes constantly out doors, but not nearly as much as some venues for dancing. In harsh sunlight, you need to use fill flash or try to shoot your subjects in areas of diffuse light. At low light level dances, even if the use of flash is permitted, you may want to use a high ISO to minimize the impact the flash will have on your subjects. Stoffen or Gary Fong filters used on your flash will give more diffuse light for most situations. Bounced flash is often used, but in order to use it well, you have to be aware of ceiling height (or bounce your light off of a white shirt (unless you can manage to get someone to hold a reflector). The lighting also determines your ISO and white balance choices.
Type of Event – This dictates your lens, shutter speed, and where you will place yourself. Shooting sports from bleachers requires a longer lens than the dance floor at a nightclub. A fast shutter speed is not often necessary to capture a politician at a campaign rally, but is required if you want to catch the water spray as a diver enters a pool. If taking candid shots, you don’t stand in the middle of the action.
ISO choice – This can be forced upon you by the lighting or speed of the action. I sometimes choose my ISO because i want the overall feeling I am attempting to achieve to be something different. I tend to shoot Swing bands and dancers using a very high ISO so I can get noise that simulates film grain, the result of which is more reminiscent of the images from the 1940′s.

Event photography for me is not simply recording an instant of time, it is making that moment’s emotional impact a bit more easily felt. The above photo would not have the same impact had I shot and processed it to be a a color, non vignetted shot.