Meeting people at shows can be a pain sometimes. I personally had trouble with it, especially in louder venues. That's why we use Meetup.com so extensively. After years of organizing meetups, here is what we've learned works best:
Why? The best time to meet people is in a more laid back environment before the show. Shows can get extremely loud. Plus, when you're at the show, most people prefer to dance, rather than talk in the back. I've personally never regretted the extra effort to find a nearby bar for us all to meet a little earlier and hang out before the show.
Meetup.com is easily the best platform for organizing events. However, it's still a terrible platform for real-time communication during the event itself. Giving away your cell phone number can get messy, especially if cell service goes down at larger events.
The solution? GroupMe! This app has been a lifesaver so many times, plus it helps us coordinate a pre-meetup location at a nearby bar a few hours before the event. The easier it is to communicate, the easier it is to make new friends.
What do I mean?
If you're at a rave, bring some kandi to give out, or bring some LED accessories to add to the vibe. LED gloves, hula hoops, poi, and much, much more are all fair game.
This applies just as much to festivals. I've seen people bring portable fans to cool people off, fun totems, epic costumes, and more. The sky's the limit with a bit of creativity. And when you're having fun and adding value, you'll be meeting people by default.
These three categories account for 95% of what I've seen work well at shows. I'll update this if I find any other good examples.