earplugs are a great idea for when it gets too loud. wear comfortable shoes and clothes, try not to be in the middle of the crowd. go with soemone else who can help you out/look out for you. try not to bring a bag with you (easily gets lost or stolen), have your phone and any other things like a wallet in your pocket with a zip or button to safely close it and even to wear a top that covers them. dont wear dangly jwelrey or anything sentimental that you'd be really upset if you lost
If it's open floor try to get there early since it fills up fast,and you want to be up close earplugs might be useful, though truthfully most people don't wear them. Only take essentials and keep them close never in a backpack, purse etc. If it's rock/metal band,There is likely going to be a moshpit, which usually happens in the middle so try to stay out of there if you rather not be pushed around.....Hope This Helped and Good Luck!
If you plan on moshing, I suggest football pads. And a helmet and mouthguard. Kidding, but seriously be careful, people will shove you. There's really not much you need to survive a hardcore concert-just wear something that makes sense (probably any black shirt) and keep some aspirin just in case ;)