The Viper Room holds several hundred, Giant several thousand. Some clubs operate daily, others only once a month, and venues change regularly. Also look for flyers at concert venues and available at some clothing stores on Melrose. Swing dancing, which became popular in LA in the 1930s, has also enjoyed a recent revival, and many Angelenos like to dress in 1950s-style clothes and go out each weekend to jive. The Derby is still the king of swing, but plenty of others have taken up the flag.
Summer is the time for the big raves.
Locations and times change often, so it is essential to pick up a local paper or flip through flyers. Cabs are also hard to find, and you can't just flag one down on the street, so don't leave your hotel without the number of a taxi company in your pocket. Some of the more upscale clubs operate a velvet rope policy. This basically means that the better you look, the more likely you will be to get in. Being female helps.