This thread has got to be a joke, right? Come on...
Erm, not if you haven't been before. If it's not a pisstake, thank god some people are considerate enough to realise if they're new they're going somewhere with a different ambience...
A few I'd say are important:
1 - It's busy, just chill a bit, you'll get there eventually. If you're really bothered, set off with loads of time to spare.
2 - If someone who is a bit rough from being hammered sits next to you, just go with it. Just because they're hammered at 3pm doesn't mean they don't have all they need in life or that they need to find something to make them happy. This comes from personal experience of hearing someone talking down to my OH a couple of years ago. People can be happy and just overdo it! Sarcasm is fine, just watch the boundaries, some people need cutting a little slack.
3 - Try to forgive the stumblers, bumpers, pint spillers etc. You can tell the dicks by sight. The genuine bumpers would be gutted if they knew you'd just walked back from a 25 minute queue and they'd knocked a drink over.
4 - People will dance like a total goon to certain stuff. Easy to deal with as you can move away when outside. When in the tents, just deal with it. You might not like someone that much, but not everyone wants to be at the front. Especially important in the tents where space is at a premium.
5 - Wherever you camp is your home. As in real life you need to deal with your neighbours in a way that either means you're now friends or you can tolerate each other. You don't have to have them round for cocktails but it's nice if they'll show an interest if you're being burgled.
Sorry quite specific ones! Most of it is common sense, which, I think, is pretty much the norm at Glasto.