Despite the overwhelmingly good advice on all sorts of live musical performances there are a few things that have not been covered.
If the venue says no smoking, obey
Despite the increasingly rude and boorish concert-goer there seems to be an uspoken rule that you can go ahead and do whatever you feel like whether it makes sense or not. Indoor venues primarily will tend to place a ban on smoking, especially for large auditorium shows. The problem is that you are not the only person who feels they have a special right to break this. It's not even as simple as not making someone else choke down your deadly second-hand smoke. What happens is that almost everyone who smokes, does, and in the end you're left with a murky enviroment largely consisting of smoke for the upper third and in many cases making it hard to see the band. Crowded outdoor venues often end in someone getting burned, literally.
If there is assigned seating, stay there
I'm not saying you can't go to the bathroom or get a drink or whatever, but do not stand for the entire concert. It's acceptable to stand when the band(s) come on or sometimes during a particular song or so, but making a habit of it is quite irritating. Not everyone wants to spend two hours standing when they bought tickets, nor did they spend the money on good seats only to be unable to see around your large, ape-like torso.
Do not push your way into your desired place in the crowd.
More an issue in smaller venues than anything. The person up front by the stage got there for a reason. They probably showed up well before you and stood around there because they wanted the space. When you and your asshole friends shove your way past halfway through the set people are not going to get out of your way no matter how much you glare at them. Drunkenly spilling the drink you just went to get doesn't help either. If you have gotten separated from your friends and are trying to get back to them or had to make an emergency run to the bathroom and want to get your place back (though in this case, it really helps if you just left and someone saw you) politely say so between songs and I'm certain people will let you through. If they don't then they're the assholes. If you're right you shouldn't have to shove.
The most important thing is to have fun, just realize that with any other case where humans have to interact the basics of rights boil down to the same thing: feel free to have fun so long as your fun doesn't disrupt things for everyone else.