There's a good reason why 75% of the posts in this thread (mine included) suggest alcohol abuse - nightclubs are rubbish.
There's nightclubs and there's nightclubs. You've got the corporate chain venues filled with the general public out on the lash. The music is typically mainly chart music and there'll be a 'smart' dress code on the door. I personally cannot stand those places, and only used them as a place to carry on drinking alcohol past closing time at the pub.
Then you've got other venues which host dance events by promoters. They typically have big name DJs playing to a large crowd who are there for the music and for the general positive friendly vibe of those sorts of events. Dress code will be extremely relaxed and alcohol probably won't be the main refreshment of choice. These are my sort of clubs. I spent many a night in them both as a paying customer and as a paid purveyor of repetitive beats.
Then you've got the lesser known, slightly seedy and unglamorous venues off the beaten track. Health and safety laws are a mere inconvenience, as are any form of functioning sewerage or respect for licensing regulations. Often good places to find really cutting edge music played by up and coming DJs and artists, or tight knit communities who love a certain genre of music, but definitely not places to flaunt anything valuable. Generally a good time to be had but with an occasional undertone of threat. I've had some amazing nights in places like this, but I've seen some messed up stuff too.
In summary, boom tish boom tish boom tish boom tish.