Get to the venue early. Even if you have seat assignments and not general admission or standing room only tickets, arrive early enough to find your seats and settle in comfortable without stepping on peoples toes to get there. If you want to stand by the front of the stage, stake your claim to the area early instead of drifting back and forth.
Minimize trips for snacks or souvenirs. Buy all your nachos, drinks and T-shirts before or after the concert, and hit the restroom at home before leaving for the show. This saves you aggravation of weaving in and out of a row of preoccupied concertgoers and saves time standing in line to use the facility when you could be watching the band.
Scan the venue rules posted on the doors leading to the auditorium. Put your camera away if the sign forbids cameras or bring it back to your car; better safe than sorry. Listen to the reasonable security guards and bouncers, but be on the lookout for power-hungry types. They're part of rock show security, too.
Behave if you're in the pit. Flail your arms, dance around, yell and have fun, but be cognizant of those around you. Give everyone enough space to move around and watch for people trying to get in or out of the standing room area.
Dress the part. If you're at a hardcore punk rock show in the pit or standing on a crowded concert floor, wear jeans or other causal attire. If you overdress, you may end up losing a high heel or get your silk jacket ripped. Remember, when in Rome behave like a Roman.