Before the event some of things to consider are the rules each festival has for what is deemed appropriate and inappropriate; these vary from festival to festival. It's important to be aware of them so you don't accidently get kicked out or ruin your time over something trivial. There are loads of online resources that offer useful tips on "surviving," the most useful ones are usually found on the festival's message boards. Especially if you're a first timer, the message boards are a great resource to ask questions or voice a concern and get feedback.
When you arrive, there will usually be a line or a wait to get in and it varies. However long it takes, you're better off just waiting quietly; the louder the crowd the slower the event staff will work. Before entering the festival grounds one thing to consider is, if you brought a bag it will most likely be checked. That being said it is not a good idea to have anything illegal on your person. Even things like cans of soda, alcohol, umbrellas, stuff like frisbees, and ciggarettes are confiscated as they can pose a hazard to others. The venue has to provide a safe environment for all attendees, which often includes younger children, so they exercise their discretion even with something like a obscene t-shirt. That being said it's best to just bring the bare essential's, if you're driving there just leave all the rest in the car.
One thing most festival goers I've spoken to have expressed anger over is the confiscation of outside alcohol. The reason for that is two fold, alcohol containers are generally glass or metal and therefore can be dangerous so they're not allowed; so if you put it into a flask or open container, that's illegal. They're also in the business of making money, so they want to sell those $10 beers inside somehow. So to avoid that you may want to consider getting drunk in the parking lot and seeing how long that'll last you.
Once inside you really shouldn't waste time figuring out where your bands are playing; some festivals offer seating. Large festivals like bamboozle can offer small cards with all the information printed on it, as well as a larger billboard display. If you're lucky all the bands you want to see will be on one stage, and your only goal then would be to get as close to the stage as possible. This can be done through a variety of ways ranging from telling people your boyfriend's aunt's besfriend's sister is all the way up front and you have to go watch her (people who use this are usually lying so it's alright to not care). To a line of people holding hands trying to push pass you like nothings going on, to people just straight up pushing you and not caring at all; the further away from the stage the less this occurs.
Needless to say you will be in a very tight situation, and when the bands come on it will only get worse. In all the excitement people will often lose sight of safety hazards they are posing by being rude and obnoxious, so you should be conscious of everything going on around you. People who are not strong enough to hold up a crowd surfing individual will just throw them, and they can come crashing down on your head. People can trip over you, your foot can get stuck under someone else's foot, etc...
If you have multiple stages to go to, you may either want to pass on one act or be able to move around so you may not want to get too close. If you do pass on seeing a certain band and do want to get close, adhere to those warnings. If you decide you can sacrifice getting close, to see all your bands, there's really not a lot to worry about. You can roam around to vendors, buy merch, talk to people that are waiting in between sets, all pretty seamlessly. You can also hear the music pretty clearly despite the fact that you may be too far away to see the band. You don't have to worry about being pushed, having other people's sweat on you, and best of all can get to the bathroom a lot easier.
With all that in mind, music festivals are a good way to kill an entire day due to travel time and how long they run. By the time you get home you will probably be exhausted, sweaty, losing your voice, can't hear too well, low on cash, and possibly sunburned (if it's a summertime festival). Despite all these cons year after year people will continue to do it again.
