I'm not going to detail a list of the best clubs in Barcelona in this post, just a few tips and pieces of information that you might need to know or that will be helpful when you go out to sample the nightlife in Barcelona.
First of all, you should know that while in English, it's normal to say "clubs" and "clubbing", in Spanish you say "discoteca". If you hop in a cab and ask the driver to take you to a "club" they'll take you to a strip joint (where the majority have those...ahem...extra services on offer, too). So, although it might remind you of when you were at high school or college, "disco" is the word.
Discos in Barcelona don't open until late, and it's often 1am before the doors open. However, most places don't start to fill up until around 2 or 3am, which is when most of the bars and pubs start to empty too.
It's also important to remember that spirits are not measured in Spain, so if you come from somewhere where optics or measuring cups are the common practice, beware, as drinks are fairly strong over here. If you usually have 3 vodka red bulls a night, you might only need 1. Clubs usually close at around 5 or 6am, and if you're still up for the party, then the "afters" will be outside with flyers, announcing the next place to continue the party.
Another big mistake people make is screwing up your entrance ticket and putting it in your back pocket for example.
Almost all entrance fees to a disco will include a drink in the price of the ticket - "una consumicion". You often either get in for free, or pay a fee (above it was 15 Euros for a recent trip to Razzmataz) with a drink included. So don't make the mistake of throwing away your ticket!
A great way to enjoy the nightlife is to rent Apartments for groups Barcelona and come along with all of your friends. For more information about Barcelona in general, and how to save money in the current crisis, check out this Budget Barcelona city guide.